diff --git a/re2/re2.cc b/re2/re2.cc
index 91d9880f4d02aa56d848b80ca69d7c2769c439d0..3285dc0954eb303961c87dc49f4b162dbcd08639 100644
--- a/re2/re2.cc
+++ b/re2/re2.cc
@@ -976,47 +976,14 @@ namespace re2
   bool RE2::CheckRewriteString(const StringPiece &rewrite,
                                std::string *error) const
   {
-    int max_token = -1;
-    for (const char *s = rewrite.data(), *end = s + rewrite.size();
-         s < end; s++)
-    {
-      int c = *s;
-      if (c != '\\')
-      {
-        continue;
-      }
-      if (++s == end)
-      {
-        *error = "Rewrite schema error: '\\' not allowed at end.";
-        return false;
-      }
-      c = *s;
-      if (c == '\\')
-      {
-        continue;
-      }
-      if (!isdigit(c))
-      {
-        *error = "Rewrite schema error: "
-                 "'\\' must be followed by a digit or '\\'.";
-        return false;
-      }
-      int n = (c - '0');
-      if (max_token < n)
-      {
-        max_token = n;
-      }
-    }
-
-    if (max_token > NumberOfCapturingGroups())
-    {
-      // *error = StringPrintf(
-      //     "Rewrite schema requests %d matches, but the regexp only has %d "
-      //     "parenthesized subexpressions.",
-      //     max_token, NumberOfCapturingGroups());
+    int num_caps = NumberOfCapturingGroups();
+    bool result = rure_check_rewrite_string(rewrite.data(), num_caps);
+    if(!result){
+      *error = "Rewrite schema error";
       return false;
     }
-    return true;
+    return true; 
+
   }
 
   // Returns the maximum submatch needed for the rewrite to be done by Replace().
diff --git a/regex-capi/include/rure.h b/regex-capi/include/rure.h
index 67194866ae31bab1343f5179f1b316710b166d07..c8e2af5162d8f1d59afa1fb9e2f45d2a5cf1bd5e 100644
--- a/regex-capi/include/rure.h
+++ b/regex-capi/include/rure.h
@@ -611,6 +611,8 @@ const char *rure_replace_all(rure *re, const uint8_t *haystack, size_t len_h,
 rure *rure_new(const uint8_t *pattern, size_t length);
 bool rure_consume(rure *re, const uint8_t *haystack, size_t length, rure_match *match);
 int rure_max_submatch(const char *rewrite);
+bool rure_check_rewrite_string(const char *rewrite, int max_token);
+
 
 #ifdef __cplusplus
 }
diff --git a/regex-capi/src/rure.rs b/regex-capi/src/rure.rs
index b88ffc4bfb5886823dd9af9b6b672c8373fb2ed0..0636326f4d2c8869b054f756fecdcfd16331472d 100644
--- a/regex-capi/src/rure.rs
+++ b/regex-capi/src/rure.rs
@@ -747,3 +747,49 @@ ffi_fn! {
         max
     }
 }
+
+ffi_fn! {
+    fn rure_check_rewrite_string(rewrite: *const c_char, cap_num: i32) -> bool {
+        let len = unsafe { CStr::from_ptr(rewrite).to_bytes().len() };
+        let pat = rewrite as *const u8;
+        let text = unsafe { slice::from_raw_parts(pat, len) };
+        let s = std::str::from_utf8(text).unwrap();
+        let mut max_token = -1;
+        let chars = s.chars().collect::<Vec<char>>();
+        let mut i = 0;
+        while i < chars.len() {
+            if chars[i] != '\\' {
+                i += 1;
+                continue;
+            }
+            i += 1;
+            
+            if i == chars.len() {
+                println!("Rewrite schema error: '\\' not allowed at end.");
+                return false;
+            }
+            // i += 1;
+            if chars[i] == '\\' {
+                i += 1;
+                continue;
+            }
+            if !chars[i].is_ascii_digit() {
+                println!("'\\' must be followed by a digit or '\\'.");
+                return false;
+            }
+            
+            let n = chars[i] as i32 - '0' as i32;
+            println!("n = {}", n);
+            i += 1;
+    
+            if n > max_token {
+                max_token = n;
+            }
+        }
+
+        if max_token > cap_num {
+            return false;
+        }
+        return true;
+    }
+}