diff --git a/make/test-guard.mk b/make/test-guard.mk
index 190841e7..db91a623 100644
--- a/make/test-guard.mk
+++ b/make/test-guard.mk
@@ -15,7 +15,7 @@ all:
 
 testability:
 	@test -f "$(TEST_GUARD)" || \
-		{ echo 'Error: Tree not testable -- run "make all" (or "make test") from the project\'s root to fix' >&2; exit 1; }
+		{ echo 'Error: Tree not testable -- run "make all" (or "make test") from project root to fix that!' >&2; exit 1; }
 
 invalidate-testability:
 	$(RM) -f "$(TEST_GUARD)"