diff --git a/packer/cache.go b/packer/cache.go
index 91fd92593..ae0c2ef6b 100644
--- a/packer/cache.go
+++ b/packer/cache.go
@@ -76,6 +76,11 @@ func (f *FileCache) cachePath(key string, hashKey string) string {
 	dotIndex := strings.LastIndex(key, ".")
 	if dotIndex > -1 {
 		suffix = key[dotIndex:len(key)]
+
+		idx := strings.Index(suffix, "?")
+		if idx != -1 {
+			suffix = suffix[0:idx]
+		}
 	}
 
 	return filepath.Join(f.CacheDir, hashKey+suffix)
diff --git a/packer/cache_test.go b/packer/cache_test.go
index 3d2ac70dc..2d76edee5 100644
--- a/packer/cache_test.go
+++ b/packer/cache_test.go
@@ -37,8 +37,13 @@ func TestFileCache(t *testing.T) {
 	defer os.RemoveAll(cacheDir)
 
 	cache := &FileCache{CacheDir: cacheDir}
-	path := cache.Lock("foo.iso")
+	path := cache.Lock("foo.ext?foo=bar")
+	defer cache.Unlock("foo.ext?foo=bar")
+	if !strings.HasSuffix(path, ".ext") {
+		t.Fatalf("bad extension with question mark: %s", path)
+	}
 
+	path = cache.Lock("foo.iso")
 	if !strings.HasSuffix(path, ".iso") {
 		t.Fatalf("path doesn't end with suffix '%s': '%s'", ".iso", path)
 	}