diff --git a/nix/ofborg-carnix.nix b/nix/ofborg-carnix.nix
index e974c8f..0094e27 100644
--- a/nix/ofborg-carnix.nix
+++ b/nix/ofborg-carnix.nix
@@ -2,12 +2,39 @@
 { lib, buildPlatform, buildRustCrate, fetchgit }:
 let kernel = buildPlatform.parsed.kernel.name;
     abi = buildPlatform.parsed.abi.name;
-    include = includedFiles: src: builtins.filterSource (path: type:
-      lib.lists.any (f:
-        let p = toString (src + ("/" + f)); in
-        (path == p) || (type == "directory" && lib.strings.hasPrefix path p)
-      ) includedFiles
-    ) src;
+    include = includedFiles: src:
+      # The comments assume the `include` field of the Cargo.toml like:
+      # include = [ "foo", "bar" ]
+      # and the package is being built from /mypackage
+      #
+      # includeFiles == [ "foo" "bar" ]
+      let
+        # and includedFileAbsolutePaths == [ "/mypackage/foo" "/mypackage/bar" ]
+        includedFileAbsolutePaths = builtins.map (relativePath: toString (src + ("/" + relativePath))) includedFiles;
+
+        # Return true only when a possible path exactly matches an
+        # absolute path, ie:
+        #
+        #     checkExactMatch "/mypackage/foo" == true
+        #     checkExactMatch "/mypackage/foo/bar" == false
+        #     checkExactMatch "/mypackage/baz" == false
+        checkExactMatch = possiblePath: builtins.elem possiblePath includedFileAbsolutePaths;
+
+        # Return true only when a possible path is a suffix to a
+        # directory described by the include.
+        #
+        #     checkPrefixMatch "/mypackage/buzfoo" == false
+        #     checkPrefixMatch "/mypackage/foo" == false
+        #     checkPrefixMatch "/mypackage/foo/bar" == true
+        #     checkPrefixMatch "/mypackage/baz/foo" == false
+        checkPrefixMatch = possiblePath: lib.lists.any
+          (acceptablePrefix: lib.strings.hasPrefix "${acceptablePrefix}/" possiblePath)
+          includedFileAbsolutePaths;
+
+      in builtins.filterSource (possiblePath: _type:
+          ((checkExactMatch possiblePath) || (checkPrefixMatch possiblePath))
+      )
+    src;
     updateFeatures = f: up: functions: builtins.deepSeq f (lib.lists.foldl' (features: fun: fun features) (lib.attrsets.recursiveUpdate f up) functions);
     mapFeatures = features: map (fun: fun { features = features; });
     mkFeatures = feat: lib.lists.foldl (features: featureName: