diff --git a/dlls/comctl32/comctl32.spec b/dlls/comctl32/comctl32.spec
index ae8e7a8b403..c13d0661882 100644
--- a/dlls/comctl32/comctl32.spec
+++ b/dlls/comctl32/comctl32.spec
@@ -74,7 +74,7 @@
 360 stdcall -noname StrCmpNW(wstr wstr long) COMCTL32_StrCmpNW
 361 stdcall -noname StrCmpNIW(wstr wstr long) COMCTL32_StrCmpNIW
 362 stdcall -noname StrStrW(wstr wstr) COMCTL32_StrStrW
-363 stub -noname StrStrIW
+363 stdcall -noname StrStrIW(wstr wstr) COMCTL32_StrStrIW
 364 stdcall -noname StrSpnW(wstr wstr) COMCTL32_StrSpnW
 365 stdcall -noname StrToIntW(wstr) COMCTL32_StrToIntW
 366 stub -noname StrChrIA
diff --git a/dlls/comctl32/comctl32undoc.c b/dlls/comctl32/comctl32undoc.c
index 9b95e9ea367..10be27b3c3b 100644
--- a/dlls/comctl32/comctl32undoc.c
+++ b/dlls/comctl32/comctl32undoc.c
@@ -2425,7 +2425,6 @@ COMCTL32_StrStrIA (LPCSTR lpStr1, LPCSTR lpStr2)
     return (NULL);
 }
 
-
 /**************************************************************************
  * StrToIntA [COMCTL32.357] Converts a string to a signed integer.
  */
@@ -2436,6 +2435,38 @@ COMCTL32_StrToIntA (LPSTR lpString)
     return atoi(lpString);
 }
 
+/**************************************************************************
+ * StrStrIW [COMCTL32.363]
+ */
+
+LPWSTR WINAPI
+COMCTL32_StrStrIW (LPCWSTR lpStr1, LPCWSTR lpStr2)
+{
+    INT len1, len2, i;
+    WCHAR  first;
+
+    if (*lpStr2 == 0)
+	return ((LPWSTR)lpStr1);
+    len1 = 0;
+    while (lpStr1[len1] != 0) ++len1;
+    len2 = 0;
+    while (lpStr2[len2] != 0) ++len2;
+    if (len2 == 0)
+	return ((LPWSTR)(lpStr1 + len1));
+    first = tolowerW (*lpStr2);
+    while (len1 >= len2) {
+	if (tolowerW (*lpStr1) == first) {
+	    for (i = 1; i < len2; ++i)
+		if (tolowerW (lpStr1[i]) != tolowerW(lpStr2[i]))
+		    break;
+	    if (i >= len2)
+		return ((LPWSTR)lpStr1);
+        }
+	++lpStr1; --len1;
+    }
+    return (NULL);
+}
+
 /**************************************************************************
  * StrToIntW [COMCTL32.365] Converts a wide char string to a signed integer.
  */