diff --git a/tools/qmake/mkspecs/features/functions.prf b/tools/qmake/mkspecs/features/functions.prf
index 88a5aad7ae3eb1a23db2e878f77b684a15360196..44ed4f9e6f64d6df606fe3b78104f76e07992c09 100644
--- a/tools/qmake/mkspecs/features/functions.prf
+++ b/tools/qmake/mkspecs/features/functions.prf
@@ -113,7 +113,11 @@ defineReplace(findOrBuildNinja) {
 
     # If we did not find ninja, then we bootstrap it.
     !exists($$out) {
-        system("python $$dirname(out)/bootstrap.py")
+        contains(DEFINES, WIN64) {
+          system("python $$dirname(out)/bootstrap.py --x64")
+        } else {
+          system("python $$dirname(out)/bootstrap.py")
+        }
     }
     return($$out)
 }