diff --git a/src/Fable.Compiler/ProjectCracker.fs b/src/Fable.Compiler/ProjectCracker.fs
index 2088cab07a..d576d11954 100644
--- a/src/Fable.Compiler/ProjectCracker.fs
+++ b/src/Fable.Compiler/ProjectCracker.fs
@@ -49,7 +49,7 @@ type CacheInfo =
             else
                 ""
 
-        IO.Path.Combine(fableModulesDir, $"project_cracked{suffix}.json")
+        IO.Path.Combine(fableModulesDir, $"project_cracked%s{suffix}.json")
 
     member this.GetTimestamp() =
         CacheInfo.GetPath(this.FableModulesDir, this.FableOptions.DebugMode)