diff --git a/lib/sources.nix b/lib/sources.nix
index 43a374c16e73..81b8a8c77178 100644
--- a/lib/sources.nix
+++ b/lib/sources.nix
@@ -43,7 +43,7 @@ let
   cleanSourceFilter =
     name: type:
     let
-      baseName = baseNameOf (toString name);
+      baseName = baseNameOf name;
     in
     !(
       # Filter out version control software files/directories
@@ -270,7 +270,7 @@ let
       filter =
         name: type:
         let
-          base = baseNameOf (toString name);
+          base = baseNameOf name;
         in
         type == "directory" || lib.any (ext: lib.hasSuffix ext base) exts;
     in
diff --git a/nixos/modules/services/hardware/fwupd.nix b/nixos/modules/services/hardware/fwupd.nix
index 1c059bf39e64..91e1afd1067e 100644
--- a/nixos/modules/services/hardware/fwupd.nix
+++ b/nixos/modules/services/hardware/fwupd.nix
@@ -35,7 +35,7 @@ let
     lib.listToAttrs (map mkEtcFile cfg.package.filesInstalledToEtc);
   extraTrustedKeys =
     let
-      mkName = p: "pki/fwupd/${baseNameOf (toString p)}";
+      mkName = p: "pki/fwupd/${baseNameOf p}";
       mkEtcFile = p: lib.nameValuePair (mkName p) { source = p; };
     in
     lib.listToAttrs (map mkEtcFile cfg.extraTrustedKeys);
diff --git a/pkgs/build-support/replace-vars/replace-vars-with.nix b/pkgs/build-support/replace-vars/replace-vars-with.nix
index c863c6fb617f..abbb9a1cc1a0 100644
--- a/pkgs/build-support/replace-vars/replace-vars-with.nix
+++ b/pkgs/build-support/replace-vars/replace-vars-with.nix
@@ -122,7 +122,7 @@ in
 
 stdenvNoCC.mkDerivation (
   {
-    name = baseNameOf (toString src);
+    name = baseNameOf src;
   }
   // optionalAttrs
   // forcedAttrs
diff --git a/pkgs/build-support/rust/build-rust-crate/test/rcgen-crates.nix b/pkgs/build-support/rust/build-rust-crate/test/rcgen-crates.nix
index 804308ed216f..563500ed0092 100644
--- a/pkgs/build-support/rust/build-rust-crate/test/rcgen-crates.nix
+++ b/pkgs/build-support/rust/build-rust-crate/test/rcgen-crates.nix
@@ -4347,7 +4347,7 @@ rec {
     sourceFilter =
       name: type:
       let
-        baseName = baseNameOf (toString name);
+        baseName = baseNameOf name;
       in
       !(
         # Filter out git
diff --git a/pkgs/build-support/substitute/substitute.nix b/pkgs/build-support/substitute/substitute.nix
index 431a97c9b1ba..050e259f4eb1 100644
--- a/pkgs/build-support/substitute/substitute.nix
+++ b/pkgs/build-support/substitute/substitute.nix
@@ -29,7 +29,7 @@
 args:
 
 let
-  name = if args ? name then args.name else baseNameOf (toString args.src);
+  name = args.name or (baseNameOf args.src);
   deprecationReplacement = lib.pipe args.replacements [
     lib.toList
     (map (lib.splitString " "))
diff --git a/pkgs/development/compilers/llvm/common/default.nix b/pkgs/development/compilers/llvm/common/default.nix
index 2a88fecc0b6e..cd15cd6f36a5 100644
--- a/pkgs/development/compilers/llvm/common/default.nix
+++ b/pkgs/development/compilers/llvm/common/default.nix
@@ -71,7 +71,7 @@ let
       ;
     src = monorepoSrc;
     versionDir =
-      (toString ../.) + "/${if (gitRelease != null) then "git" else lib.versions.major release_version}";
+      ../. + "/${if (gitRelease != null) then "git" else lib.versions.major release_version}";
     getVersionFile =
       p:
       builtins.path {
@@ -95,15 +95,12 @@ let
               matchBefore && matchAfter;
 
             patchDir =
-              toString
-                (
-                  if constraints == null then
-                    { path = metadata.versionDir; }
-                  else
-                    (lib.findFirst matchConstraint { path = metadata.versionDir; } constraints)
-                ).path;
+              if constraints == null then
+                metadata.versionDir
+              else
+                (lib.findFirst matchConstraint { path = metadata.versionDir; } constraints).path;
           in
-          "${patchDir}/${p}";
+          patchDir + ("/" + p);
       };
   };
 
diff --git a/pkgs/kde/plasma/breeze-plymouth/default.nix b/pkgs/kde/plasma/breeze-plymouth/default.nix
index d85dd1861a10..ccb7c6d9d3f0 100644
--- a/pkgs/kde/plasma/breeze-plymouth/default.nix
+++ b/pkgs/kde/plasma/breeze-plymouth/default.nix
@@ -26,7 +26,7 @@ let
   ];
   resolvedLogoName =
     if (logoFile != null && logoName == null) then
-      lib.strings.removeSuffix ".png" (baseNameOf (toString logoFile))
+      lib.strings.removeSuffix ".png" (baseNameOf logoFile)
     else
       logoName;
 in