diff --git a/dlls/shlwapi/string.c b/dlls/shlwapi/string.c
index b4b5b8af537..eaaaf3bd2ab 100644
--- a/dlls/shlwapi/string.c
+++ b/dlls/shlwapi/string.c
@@ -364,7 +364,7 @@ int WINAPI StrCmpIW(LPCWSTR lpszStr, LPCWSTR lpszComp)
  * PARAMS
  *  lpszStr  [I] First string to compare
  *  lpszComp [I] Second string to compare
- *  iLen     [I] Maximum number of chars to compare.
+ *  iLen     [I] Number of chars to compare
  *
  * RETURNS
  *  An integer less than, equal to or greater than 0, indicating that
@@ -395,7 +395,7 @@ INT WINAPI StrCmpNW(LPCWSTR lpszStr, LPCWSTR lpszComp, INT iLen)
  * PARAMS
  *  lpszStr  [I] First string to compare
  *  lpszComp [I] Second string to compare
- *  iLen     [I] Maximum number of chars to compare.
+ *  iLen     [I] Number of chars to compare
  *
  * RETURNS
  *  An integer less than, equal to or greater than 0, indicating that
@@ -521,13 +521,15 @@ static LPSTR SHLWAPI_StrStrHelperA(LPCSTR lpszStr, LPCSTR lpszSearch,
                                    INT (WINAPI *pStrCmpFn)(LPCSTR,LPCSTR,INT))
 {
   size_t iLen;
+  LPCSTR end;
 
   if (!lpszStr || !lpszSearch || !*lpszSearch)
     return NULL;
 
   iLen = strlen(lpszSearch);
+  end = lpszStr + strlen(lpszStr);
 
-  while (*lpszStr)
+  while (lpszStr + iLen <= end)
   {
     if (!pStrCmpFn(lpszStr, lpszSearch, iLen))
       return (LPSTR)lpszStr;
@@ -670,6 +672,7 @@ LPSTR WINAPI StrStrIA(LPCSTR lpszStr, LPCSTR lpszSearch)
 LPWSTR WINAPI StrStrIW(LPCWSTR lpszStr, LPCWSTR lpszSearch)
 {
   int iLen;
+  LPCWSTR end;
 
   TRACE("(%s,%s)\n", debugstr_w(lpszStr), debugstr_w(lpszSearch));
 
@@ -677,8 +680,9 @@ LPWSTR WINAPI StrStrIW(LPCWSTR lpszStr, LPCWSTR lpszSearch)
     return NULL;
 
   iLen = strlenW(lpszSearch);
+  end = lpszStr + strlenW(lpszStr);
 
-  while (*lpszStr)
+  while (lpszStr + iLen <= end)
   {
     if (!StrCmpNIW(lpszStr, lpszSearch, iLen))
       return (LPWSTR)lpszStr;