diff --git a/dlls/crypt32/protectdata.c b/dlls/crypt32/protectdata.c
index a1a3369dcb5..3ecd35bec50 100644
--- a/dlls/crypt32/protectdata.c
+++ b/dlls/crypt32/protectdata.c
@@ -1015,6 +1015,11 @@ BOOL WINAPI CryptUnprotectData(DATA_BLOB* pDataIn,
         SetLastError(ERROR_INVALID_PARAMETER);
         goto finished;
     }
+    if (!pDataIn->cbData)
+    {
+        SetLastError(ERROR_INVALID_DATA);
+        goto finished;
+    }
 
     /* debug: show our arguments */
     report(pDataIn,pOptionalEntropy,pPromptStruct,dwFlags);