diff --git a/tests/util.py b/tests/util.py
index 3e5d25fb0ff..27acba404e7 100644
--- a/tests/util.py
+++ b/tests/util.py
@@ -35,7 +35,7 @@
 
 def _assert_format_equal(expected: str, actual: str) -> None:
     ast_print = not os.environ.get("SKIP_AST_PRINT")
-    ast_print_diff = os.environ.get("SKIP_AST_PRINT_DIFF")
+    ast_print_diff = not os.environ.get("SKIP_AST_PRINT_DIFF")
     if actual != expected and (ast_print or ast_print_diff):
         bdv: DebugVisitor[Any]
         actual_out: str = ""