diff --git a/src/platform/cocoamain.mm b/src/platform/cocoamain.mm
index d9c12654..9838058a 100644
--- a/src/platform/cocoamain.mm
+++ b/src/platform/cocoamain.mm
@@ -792,6 +792,9 @@ bool SolveSpace::GetSaveFile(std::string *file, const std::string &defExtension,
     if(defExtension != "") {
         extensionIndex = [extensions indexOfObject:
             [NSString stringWithUTF8String:defExtension.c_str()]];
+        if(extensionIndex == -1) {
+            extensionIndex = 0;
+        }
     }
 
     [button selectItemAtIndex:extensionIndex];