diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 33aa29f3a..0daeea77c 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2022,8 +2022,13 @@ static void prim_dirOf(EvalState & state, const PosIdx pos, Value ** args, Value
         NixStringContext context;
         auto path = state.coerceToString(
             pos, *args[0], context, "while evaluating the first argument passed to 'builtins.dirOf'", false, false);
-        auto dir = dirOf(*path);
-        v.mkString(dir, context);
+        auto pos = path->rfind('/');
+        if (pos == path->npos)
+            v.mkStringMove(".", context);
+        else if (pos == 0)
+            v.mkStringMove("/", context);
+        else
+            v.mkString(path->substr(0, pos), context);
     }
 }
 
diff --git a/tests/functional/lang/eval-okay-builtins-dirOf.exp b/tests/functional/lang/eval-okay-builtins-dirOf.exp
new file mode 100644
index 000000000..e0093e93a
--- /dev/null
+++ b/tests/functional/lang/eval-okay-builtins-dirOf.exp
@@ -0,0 +1 @@
+{ pathDoesntExistNested1 = /totallydoesntexistreally; pathDoesntExistNested2 = /totallydoesntexistreally/subdir1; pathDoesntExistRoot = /; pathRoot = /; stringEmpty = "."; stringMultipleSeps = "a//"; stringNoSep = "."; stringRoot = "/"; stringRootA = "/"; stringRootSlash = "/"; stringRootSlashSlash = "//"; stringSingleDir = "a"; stringWithDot = "a/b/c/."; stringWithDotAndDotDot = "a/b/c/../."; stringWithDotAndDotDotSep2 = "a/b/c/.././"; stringWithDotDot = "a/b/c/.."; stringWithDotDotSep2 = "a/b/c/../"; stringWithDotSep2 = "a/b/c/./"; }
diff --git a/tests/functional/lang/eval-okay-builtins-dirOf.nix b/tests/functional/lang/eval-okay-builtins-dirOf.nix
new file mode 100644
index 000000000..d2eae1c4e
--- /dev/null
+++ b/tests/functional/lang/eval-okay-builtins-dirOf.nix
@@ -0,0 +1,21 @@
+{
+  stringEmpty = dirOf "";
+  stringNoSep = dirOf "filename";
+  stringSingleDir = dirOf "a/b";
+  stringMultipleSeps = dirOf "a///b";
+  stringRoot = dirOf "/";
+  stringRootSlash = dirOf "//";
+  stringRootSlashSlash = dirOf "///";
+  stringRootA = dirOf "/a";
+  stringWithDot = dirOf "a/b/c/./d";
+  stringWithDotSep2 = dirOf "a/b/c/.//d";
+  stringWithDotDot = dirOf "a/b/c/../d";
+  stringWithDotDotSep2 = dirOf "a/b/c/..//d";
+  stringWithDotAndDotDot = dirOf "a/b/c/.././d";
+  stringWithDotAndDotDotSep2 = dirOf "a/b/c/.././/d";
+
+  pathRoot = dirOf /.;
+  pathDoesntExistRoot = dirOf /totallydoesntexistreally;
+  pathDoesntExistNested1 = dirOf /totallydoesntexistreally/subdir1;
+  pathDoesntExistNested2 = dirOf /totallydoesntexistreally/subdir1/subdir2;
+}