diff --git a/Src/IronPythonTest/Cases/IronPythonCasesManifest.ini b/Src/IronPythonTest/Cases/IronPythonCasesManifest.ini
index 56c38a74e..f63aa1863 100644
--- a/Src/IronPythonTest/Cases/IronPythonCasesManifest.ini
+++ b/Src/IronPythonTest/Cases/IronPythonCasesManifest.ini
@@ -56,6 +56,8 @@ Reason=Assertion error
 
 [IronPython.test_memory]
 IsolationLevel=PROCESS # to avoid having a long list of object subtypes
+RunCondition=NOT $(IS_MONO)
+Reason=Memory allocation on Mono may not match MS.NET
 
 [IronPython.test_number]
 Timeout=300000 # 5 minute timeout - slow on macOS