diff --git a/clang/docs/ClangFormat.rst b/clang/docs/ClangFormat.rst
--- a/clang/docs/ClangFormat.rst
+++ b/clang/docs/ClangFormat.rst
@@ -31,12 +31,13 @@
   Clang-format options:
 
     --Werror                   - If set, changes formatting warnings to errors
-    --Wno-error=unknown        - If set, unknown format options are only warned about.
-                                 This can be used to enable formatting, even if the
-                                 configuration contains unknown (newer) options.
-                                 Use with caution, as this might lead to dramatically
-                                 differing format depending on an option being
-                                 supported or not.
+    --Wno-error=<value>        - If set don't error out on the specified warning type.
+      =unknown                 -   If set, unknown format options are only warned about.
+                                   This can be used to enable formatting, even if the
+                                   configuration contains unknown (newer) options.
+                                   Use with caution, as this might lead to dramatically
+                                   differing format depending on an option being
+                                   supported or not.
     --assume-filename=<string> - Override filename used to determine the language.
                                  When reading from stdin, clang-format assumes this
                                  filename to determine the language.
diff --git a/clang/test/Format/error-config.cpp b/clang/test/Format/error-config.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Format/error-config.cpp
@@ -0,0 +1,11 @@
+// RUN: clang-format %s --Wno-error=unknown --style="{UnknownKey: true}" 2>&1 | FileCheck %s -check-prefix=CHECK
+// RUN: not clang-format %s --style="{UnknownKey: true}" 2>&1 | FileCheck %s -check-prefix=CHECK-FAIL
+
+// CHECK: YAML:1:2: warning: unknown key 'UnknownKey'
+// CHECK-NEXT: {UnknownKey: true}
+// CHECK-NEXT: ^~~~~~~~~~
+// CHECK-FAIL: YAML:1:2: error: unknown key 'UnknownKey'
+// CHECK-FAIL-NEXT: {UnknownKey: true}
+// CHECK-FAIL-NEXT: ^~~~~~~~~~
+
+int i ;
diff --git a/clang/tools/clang-format/ClangFormat.cpp b/clang/tools/clang-format/ClangFormat.cpp
--- a/clang/tools/clang-format/ClangFormat.cpp
+++ b/clang/tools/clang-format/ClangFormat.cpp
@@ -104,18 +104,6 @@
              "SortIncludes style flag"),
     cl::cat(ClangFormatCategory));
 
-// using the full param name as Wno-error probably won't be a common use case in
-// clang-format
-static cl::opt<bool> AllowUnknownOptions(
-    "Wno-error=unknown",
-    cl::desc("If set, unknown format options are only warned about.\n"
-             "This can be used to enable formatting, even if the\n"
-             "configuration contains unknown (newer) options.\n"
-             "Use with caution, as this might lead to dramatically\n"
-             "differing format depending on an option being\n"
-             "supported or not."),
-    cl::init(false), cl::cat(ClangFormatCategory));
-
 static cl::opt<bool>
     Verbose("verbose", cl::desc("If set, shows the list of processed files"),
             cl::cat(ClangFormatCategory));
@@ -156,6 +144,23 @@
                      cl::desc("If set, changes formatting warnings to errors"),
                      cl::cat(ClangFormatCategory));
 
+namespace {
+enum class WNoError { Unknown };
+}
+
+static cl::bits<WNoError> WNoErrorList(
+    "Wno-error",
+    cl::desc("If set don't error out on the specified warning type."),
+    cl::values(
+        clEnumValN(WNoError::Unknown, "unknown",
+                   "If set, unknown format options are only warned about.\n"
+                   "This can be used to enable formatting, even if the\n"
+                   "configuration contains unknown (newer) options.\n"
+                   "Use with caution, as this might lead to dramatically\n"
+                   "differing format depending on an option being\n"
+                   "supported or not.")),
+    cl::cat(ClangFormatCategory));
+
 static cl::opt<bool>
     ShowColors("fcolor-diagnostics",
                cl::desc("If set, and on a color-capable terminal controls "
@@ -391,7 +396,7 @@
 
   llvm::Expected<FormatStyle> FormatStyle =
       getStyle(Style, AssumedFileName, FallbackStyle, Code->getBuffer(),
-               nullptr, AllowUnknownOptions.getValue());
+               nullptr, WNoErrorList.isSet(WNoError::Unknown));
   if (!FormatStyle) {
     llvm::errs() << llvm::toString(FormatStyle.takeError()) << "\n";
     return true;