diff --git a/lib/checkbufferoverrun.cpp b/lib/checkbufferoverrun.cpp
index 4216a5977..af9969dfb 100644
--- a/lib/checkbufferoverrun.cpp
+++ b/lib/checkbufferoverrun.cpp
@@ -1540,13 +1540,7 @@ void CheckBufferOverrun::checkStringArgument()
                 const std::list<Library::ArgumentChecks::MinSize> *minsizes = _settings->library.argminsizes(tok->str(), argnr);
                 if (!minsizes)
                     continue;
-                unsigned int sizeofstring = 1;
-                for (unsigned int i = 0U; i < argtok->str().size(); i++) {
-                    if (argtok->str()[i] == '\\')
-                        ++i;
-                    ++sizeofstring;
-                }
-                if (checkMinSizes(*minsizes, tok, sizeofstring, nullptr))
+                if (checkMinSizes(*minsizes, tok, Token::getStrSize(argtok), nullptr))
                     bufferOverrunError(argtok);
             }
         }
diff --git a/lib/token.cpp b/lib/token.cpp
index d2ff0bf1d..18a39fbd9 100644
--- a/lib/token.cpp
+++ b/lib/token.cpp
@@ -651,6 +651,19 @@ std::size_t Token::getStrLength(const Token *tok)
     return len;
 }
 
+std::size_t Token::getStrSize(const Token *tok)
+{
+    assert(tok != nullptr && tok->type() == eString);
+    const std::string &str = tok->str();
+    unsigned int sizeofstring = 1U;
+    for (unsigned int i = 1U; i < str.size() - 1U; i++) {
+        if (str[i] == '\\')
+            ++i;
+        ++sizeofstring;
+    }
+    return sizeofstring;
+}
+
 std::string Token::getCharAt(const Token *tok, std::size_t index)
 {
     assert(tok != nullptr);
diff --git a/lib/token.h b/lib/token.h
index 341479ffb..ed35d586a 100644
--- a/lib/token.h
+++ b/lib/token.h
@@ -197,6 +197,15 @@ public:
      **/
     static std::size_t getStrLength(const Token *tok);
 
+    /**
+     * @return sizeof of C-string.
+     *
+     * Should be called for %%str%% tokens only.
+     *
+     * @param tok token with C-string
+     **/
+    static std::size_t getStrSize(const Token *tok);
+
     /**
      * @return char of C-string at index (possible escaped "\\n")
      *
diff --git a/test/testtoken.cpp b/test/testtoken.cpp
index 4179ef069..8398a8ea3 100644
--- a/test/testtoken.cpp
+++ b/test/testtoken.cpp
@@ -48,6 +48,7 @@ private:
         TEST_CASE(multiCompare4);
         TEST_CASE(multiCompare5);
         TEST_CASE(getStrLength);
+        TEST_CASE(getStrSize);
         TEST_CASE(strValue);
 
         TEST_CASE(deleteLast);
@@ -266,6 +267,19 @@ private:
         ASSERT_EQUALS(1, (int)Token::getStrLength(&tok));
     }
 
+    void getStrSize() const {
+        Token tok(0);
+
+        tok.str("\"abc\"");
+        ASSERT_EQUALS(sizeof("abc"), Token::getStrSize(&tok));
+
+        tok.str("\"\\0abc\"");
+        ASSERT_EQUALS(sizeof("\0abc"), Token::getStrSize(&tok));
+
+        tok.str("\"\\\\\"");
+        ASSERT_EQUALS(sizeof("\\"), Token::getStrSize(&tok));
+    }
+
     void strValue() const {
         Token tok(0);
         tok.str("\"\"");