diff --git a/dlls/wininet/http.c b/dlls/wininet/http.c
index db85d0b7535..70d5f2e94d2 100644
--- a/dlls/wininet/http.c
+++ b/dlls/wininet/http.c
@@ -6071,3 +6071,12 @@ BOOL WINAPI InternetShowSecurityInfoByURLW(LPCWSTR url, HWND window)
    FIXME("stub: %s %p\n", debugstr_w(url), window);
    return FALSE;
 }
+
+/***********************************************************************
+ *           ShowX509EncodedCertificate (@)
+ */
+DWORD WINAPI ShowX509EncodedCertificate(HWND parent, LPBYTE cert, DWORD len)
+{
+   FIXME("stub: %p %p %u\n", parent, cert, len);
+   return ERROR_CALL_NOT_IMPLEMENTED;
+}
diff --git a/dlls/wininet/wininet.spec b/dlls/wininet/wininet.spec
index 583b7ba798f..82b0d7d4ff5 100644
--- a/dlls/wininet/wininet.spec
+++ b/dlls/wininet/wininet.spec
@@ -236,7 +236,7 @@
 @ stub ShowCertificate
 @ stub ShowClientAuthCerts
 @ stub ShowSecurityInfo
-@ stub ShowX509EncodedCertificate
+@ stdcall ShowX509EncodedCertificate(ptr ptr long)
 @ stdcall UnlockUrlCacheEntryFile(str long) UnlockUrlCacheEntryFileA
 @ stdcall UnlockUrlCacheEntryFileA(str long)
 @ stdcall UnlockUrlCacheEntryFileW(wstr long)