diff --git a/lib/path/tests/default.nix b/lib/path/tests/default.nix
index 9a31e42828f48..6b8e515f43304 100644
--- a/lib/path/tests/default.nix
+++ b/lib/path/tests/default.nix
@@ -24,8 +24,9 @@ pkgs.runCommand "lib-path-tests" {
   export TEST_LIB=$PWD/lib
 
   echo "Running unit tests lib/path/tests/unit.nix"
-  nix-instantiate --eval lib/path/tests/unit.nix \
-    --argstr libpath "$TEST_LIB"
+  nix-instantiate --eval --show-trace \
+    --argstr libpath "$TEST_LIB" \
+    lib/path/tests/unit.nix
 
   echo "Running property tests lib/path/tests/prop.sh"
   bash lib/path/tests/prop.sh ${toString seed}
diff --git a/lib/path/tests/prop.sh b/lib/path/tests/prop.sh
index e48c6667fa08f..9fea521577836 100755
--- a/lib/path/tests/prop.sh
+++ b/lib/path/tests/prop.sh
@@ -71,7 +71,7 @@ fi
 
 # Precalculate all normalisations with a single Nix call. Calling Nix for each
 # string individually would take way too long
-nix-instantiate --eval --strict --json \
+nix-instantiate --eval --strict --json --show-trace \
     --argstr libpath "$TEST_LIB" \
     --argstr dir "$tmp/strings" \
     "$SCRIPT_DIR"/prop.nix \