diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2901,10 +2901,6 @@
   }
   FormatStyle Style = getLLVMStyle(guessLanguage(FileName, Code));
 
-  FormatStyle FallbackStyle = getNoStyle();
-  if (!getPredefinedStyle(FallbackStyleName, Style.Language, &FallbackStyle))
-    return make_string_error("Invalid fallback style \"" + FallbackStyleName);
-
   if (StyleName.startswith("{")) {
     // Parse YAML/JSON style from the command line.
     if (std::error_code ec = parseConfiguration(
@@ -2974,6 +2970,10 @@
     return make_string_error("Configuration file(s) do(es) not support " +
                              getLanguageName(Style.Language) + ": " +
                              UnsuitableConfigFiles);
+
+  FormatStyle FallbackStyle = getNoStyle();
+  if (!getPredefinedStyle(FallbackStyleName, Style.Language, &FallbackStyle))
+    return make_string_error("Invalid fallback style \"" + FallbackStyleName);
   return FallbackStyle;
 }
 
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -17861,11 +17861,17 @@
   ASSERT_TRUE((bool)Style3);
   ASSERT_EQ(*Style3, getGoogleStyle());
 
-  // Test 4: error on invalid fallback style
+  // Test 4.1: error on invalid fallback style
   auto Style4 = getStyle("file", "a.h", "KungFu", "", &FS);
   ASSERT_FALSE((bool)Style4);
   llvm::consumeError(Style4.takeError());
 
+  // Test 4.2: don't error on invalid fallback style, if it is not going to be
+  // used.
+  Style4 = getStyle("file", "/a/a.h", "KungFu", "", &FS);
+  ASSERT_TRUE((bool)Style4);
+  ASSERT_EQ(*Style4, getLLVMStyle());
+
   // Test 5: error on invalid yaml on command line
   auto Style5 = getStyle("{invalid_key=invalid_value}", "a.h", "LLVM", "", &FS);
   ASSERT_FALSE((bool)Style5);