diff --git a/libfuse/include/fuse_common.h b/libfuse/include/fuse_common.h
index 573f55d4..e631c056 100644
--- a/libfuse/include/fuse_common.h
+++ b/libfuse/include/fuse_common.h
@@ -133,6 +133,7 @@ struct fuse_file_info_t
 #define FUSE_CAP_PASSTHROUGH          (1ULL << 25)
 #define FUSE_CAP_HANDLE_KILLPRIV      (1ULL << 26)
 #define FUSE_CAP_HANDLE_KILLPRIV_V2   (1ULL << 27)
+#define FUSE_CAP_ALLOW_IDMAP          (1ULL << 28)
 
 /**
  * Ioctl flags
diff --git a/libfuse/lib/fuse_lowlevel.cpp b/libfuse/lib/fuse_lowlevel.cpp
index 6af3130c..a7a8fdca 100644
--- a/libfuse/lib/fuse_lowlevel.cpp
+++ b/libfuse/lib/fuse_lowlevel.cpp
@@ -1203,6 +1203,8 @@ do_init(fuse_req_t             req,
         f->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
       if(inargflags & FUSE_HANDLE_KILLPRIV_V2)
         f->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV_V2;
+      if(inargflags & FUSE_ALLOW_IDMAP)
+        f->conn.capable |= FUSE_CAP_ALLOW_IDMAP;
     }
   else
     {
@@ -1280,6 +1282,9 @@ do_init(fuse_req_t             req,
     outargflags |= FUSE_HANDLE_KILLPRIV;
   if(f->conn.want & FUSE_CAP_HANDLE_KILLPRIV_V2)
     outargflags |= FUSE_HANDLE_KILLPRIV_V2;
+  if(f->conn.want & FUSE_CAP_ALLOW_IDMAP)
+    outargflags |= FUSE_ALLOW_IDMAP;
+
   if(f->conn.want & FUSE_CAP_PASSTHROUGH)
     {
       outargflags |= FUSE_PASSTHROUGH;
diff --git a/mkdocs/docs/config/kernel-permissions-check.md b/mkdocs/docs/config/kernel-permissions-check.md
index 547c818a..c4fb253e 100644
--- a/mkdocs/docs/config/kernel-permissions-check.md
+++ b/mkdocs/docs/config/kernel-permissions-check.md
@@ -16,4 +16,4 @@ help. Like [export-support](export-support.md) this is mostly for
 debugging.
 
 This option is a kernel mount option so unable to be changed at
-runtime.
+runtime. It controls the `default_permissions` FUSE kernel option.
diff --git a/mkdocs/docs/config/options.md b/mkdocs/docs/config/options.md
index 8a282dad..5695e98e 100644
--- a/mkdocs/docs/config/options.md
+++ b/mkdocs/docs/config/options.md
@@ -86,6 +86,9 @@ config file.
 * **[export-support](export-support.md)=BOOL**: Sets a low-level FUSE
   feature intended to indicate the filesystem can support being
   exported via NFS. (default: true)
+* **[kernel-permissions-check](kernel-permissions-check.md)=BOOL**:
+  Controls the FUSE `default_permissions` option. Primarily for
+  debugging. (default: true)
 * **security_capability=BOOL**: If false return ENOATTR when xattr
   security.capability is queried. (default: true)
 * **[xattr](xattr.md)=passthrough|noattr|nosys**: Runtime control of
diff --git a/mkdocs/docs/faq/technical_behavior_and_limitations.md b/mkdocs/docs/faq/technical_behavior_and_limitations.md
index 50dfc3a0..136aaa0d 100644
--- a/mkdocs/docs/faq/technical_behavior_and_limitations.md
+++ b/mkdocs/docs/faq/technical_behavior_and_limitations.md
@@ -201,3 +201,15 @@ contention and therefore lower performance than Linux.
 Additionally, mergerfs [utilizes a cache for supplemental
 groups](../known_issues_bugs.md#supplemental-user-groups) due the the
 high cost of querying that information.
+
+
+## Does mergerfs support idmap?
+
+Yes. At least in so far as it's been enabled now the FUSE itself
+allows a filesystem to indicate it is allowed.
+
+Requires that
+[kernel-permissions-check](../config/kernel-permissions-check.md) be
+enabled (the default.)
+
+If there are any usage issues contact the [author](../support.md).
diff --git a/src/fuse_init.cpp b/src/fuse_init.cpp
index 84d1c49b..d99d95ea 100644
--- a/src/fuse_init.cpp
+++ b/src/fuse_init.cpp
@@ -206,6 +206,7 @@ FUSE::init(fuse_conn_info *conn_)
   ::_want_if_capable(conn_,FUSE_CAP_POSIX_ACL,&cfg.posix_acl);
   ::_want_if_capable(conn_,FUSE_CAP_READDIR_PLUS,&cfg.readdirplus);
   ::_want_if_capable(conn_,FUSE_CAP_WRITEBACK_CACHE,&cfg.writeback_cache);
+  ::_want_if_capable(conn_,FUSE_CAP_ALLOW_IDMAP);
   //    ::_want_if_capable(conn_,FUSE_CAP_READDIR_PLUS_AUTO);
   ::_want_if_capable_max_pages(conn_,cfg);
   conn_->want &= ~FUSE_CAP_POSIX_LOCKS;
diff --git a/src/mergerfs.cpp b/src/mergerfs.cpp
index 5cd44136..fbf4a32b 100644
--- a/src/mergerfs.cpp
+++ b/src/mergerfs.cpp
@@ -362,7 +362,7 @@ int
 _pick_app_and_run(int    argc_,
                   char **argv_)
 {
-  std::filesystem::path appname;
+  fs::path appname;
 
   appname = argv_[0];
   appname = appname.filename();
diff --git a/src/policy.hpp b/src/policy.hpp
index 7c7341ce..58707d53 100644
--- a/src/policy.hpp
+++ b/src/policy.hpp
@@ -64,9 +64,9 @@ namespace Policy
     }
 
     int
-    operator()(const Branches::Ptr         &branches_,
-               const std::filesystem::path &fusepath_,
-               std::vector<Branch*>        &output_) const
+    operator()(const Branches::Ptr  &branches_,
+               const fs::path       &fusepath_,
+               std::vector<Branch*> &output_) const
     {
       return (*impl)(branches_,fusepath_,output_);
     }
@@ -92,7 +92,7 @@ namespace Policy
     std::string name;
     virtual bool path_preserving(void) const = 0;
     virtual int operator()(const Branches::Ptr&,
-                           const std::filesystem::path&,
+                           const fs::path&,
                            std::vector<Branch*>&) const = 0;
   };
 
@@ -124,9 +124,9 @@ namespace Policy
     }
 
     int
-    operator()(const Branches::Ptr         &branches_,
-               const std::filesystem::path &fusepath_,
-               std::vector<Branch*>        &output_) const
+    operator()(const Branches::Ptr  &branches_,
+               const fs::path       &fusepath_,
+               std::vector<Branch*> &output_) const
     {
       return (*impl)(branches_,fusepath_,output_);
     }
@@ -151,7 +151,7 @@ namespace Policy
   public:
     std::string name;
     virtual int operator()(const Branches::Ptr&,
-                           const std::filesystem::path&,
+                           const fs::path&,
                            std::vector<Branch*>&) const = 0;
   };
 
@@ -178,7 +178,7 @@ namespace Policy
 
     int
     operator()(const Branches::Ptr  &branches_,
-               const std::filesystem::path &fusepath_,
+               const fs::path       &fusepath_,
                std::vector<Branch*> &output_) const
     {
       return (*impl)(branches_,fusepath_,output_);
diff --git a/src/policy_all.hpp b/src/policy_all.hpp
index 46e696f3..8cafc4a2 100644
--- a/src/policy_all.hpp
+++ b/src/policy_all.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return false; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_epall.hpp b/src/policy_epall.hpp
index 9e5eda10..96da8637 100644
--- a/src/policy_epall.hpp
+++ b/src/policy_epall.hpp
@@ -34,7 +34,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -48,7 +48,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -63,7 +63,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_epff.hpp b/src/policy_epff.hpp
index c86652a2..385cee15 100644
--- a/src/policy_epff.hpp
+++ b/src/policy_epff.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_eplfs.hpp b/src/policy_eplfs.hpp
index 0ead02bf..f18a538c 100644
--- a/src/policy_eplfs.hpp
+++ b/src/policy_eplfs.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_eplus.hpp b/src/policy_eplus.hpp
index 410f60d3..a28eb4f2 100644
--- a/src/policy_eplus.hpp
+++ b/src/policy_eplus.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_epmfs.hpp b/src/policy_epmfs.hpp
index 8dc26908..85eb0537 100644
--- a/src/policy_epmfs.hpp
+++ b/src/policy_epmfs.hpp
@@ -34,7 +34,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -48,7 +48,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -63,7 +63,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_eppfrd.hpp b/src/policy_eppfrd.hpp
index 0f431792..20a1f173 100644
--- a/src/policy_eppfrd.hpp
+++ b/src/policy_eppfrd.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_eprand.hpp b/src/policy_eprand.hpp
index aeb87a0d..9e8ea8a4 100644
--- a/src/policy_eprand.hpp
+++ b/src/policy_eprand.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return true; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_erofs.hpp b/src/policy_erofs.hpp
index d4e8d798..a0bdb1ed 100644
--- a/src/policy_erofs.hpp
+++ b/src/policy_erofs.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving(void) const final { return false; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_ff.hpp b/src/policy_ff.hpp
index 5ddc622c..c28f75ef 100644
--- a/src/policy_ff.hpp
+++ b/src/policy_ff.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -47,7 +47,7 @@ namespace Policy
     public:
       bool path_preserving(void) const final { return false; }
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
 
     };
@@ -61,7 +61,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_lfs.hpp b/src/policy_lfs.hpp
index 37d35856..370fde16 100644
--- a/src/policy_lfs.hpp
+++ b/src/policy_lfs.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving() const final { return false; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/policy_lus.hpp b/src/policy_lus.hpp
index 23755790..a26f4b67 100644
--- a/src/policy_lus.hpp
+++ b/src/policy_lus.hpp
@@ -33,7 +33,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
 
@@ -46,7 +46,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
       bool path_preserving() const final { return false; }
     };
@@ -60,7 +60,7 @@ namespace Policy
 
     public:
       int operator()(const Branches::Ptr&,
-                     const std::filesystem::path&,
+                     const fs::path&,
                      std::vector<Branch*>&) const final;
     };
   }
diff --git a/src/to_string.cpp b/src/to_string.cpp
index 241b89c8..94b3043e 100644
--- a/src/to_string.cpp
+++ b/src/to_string.cpp
@@ -55,7 +55,7 @@ str::to(const std::string &s_)
 }
 
 std::string
-str::to(const std::filesystem::path &path_)
+str::to(const fs::path &path_)
 {
   return path_.string();
 }
diff --git a/src/to_string.hpp b/src/to_string.hpp
index 8a7b55af..18561bef 100644
--- a/src/to_string.hpp
+++ b/src/to_string.hpp
@@ -18,6 +18,8 @@
 
 #pragma once
 
+#include "fs_path.hpp"
+
 #include <cstdint>
 #include <filesystem>
 #include <string>
@@ -30,5 +32,5 @@ namespace str
   std::string to(const uint64_t);
   std::string to(const int64_t);
   std::string to(const std::string&);
-  std::string to(const std::filesystem::path&);
+  std::string to(const fs::path&);
 }