diff --git a/dlls/mlang/mlang.c b/dlls/mlang/mlang.c
index 7eb2d235b8a..bff21484435 100644
--- a/dlls/mlang/mlang.c
+++ b/dlls/mlang/mlang.c
@@ -549,6 +549,24 @@ HRESULT WINAPI IsConvertINetStringAvailable(
     return S_FALSE;
 }
 
+HRESULT WINAPI LcidToRfc1766A(
+    LCID Locale,
+    LPSTR pszRfc1766,
+    INT nChar)
+{
+    FIXME("%ld %s %u\n", Locale, pszRfc1766, nChar);
+    return S_FALSE;
+}
+
+HRESULT WINAPI LcidToRfc1766W(
+    LCID Locale,
+    LPWSTR pszRfc1766,
+    INT nChar)
+{
+    FIXME("%ld %p %u\n", Locale, pszRfc1766, nChar);
+    return S_FALSE;
+}
+
 /******************************************************************************
  * MLANG ClassFactory
  */
diff --git a/dlls/mlang/mlang.spec b/dlls/mlang/mlang.spec
index c5ecea61b6c..3f7d7631bf1 100644
--- a/dlls/mlang/mlang.spec
+++ b/dlls/mlang/mlang.spec
@@ -8,7 +8,7 @@
 @ stdcall DllUnregisterServer() MLANG_DllUnregisterServer
 @ stub GetGlobalFontLinkObject
 @ stdcall IsConvertINetStringAvailable(long long)
-@ stub LcidToRfc1766A
-@ stub LcidToRfc1766W
+@ stdcall LcidToRfc1766A(long ptr long)
+@ stdcall LcidToRfc1766W(long ptr long)
 @ stub Rfc1766ToLcidA
 @ stub Rfc1766ToLcidW