diff --git a/cfg/windows.cfg b/cfg/windows.cfg
index 50ea2b6af..7ee2fd616 100644
--- a/cfg/windows.cfg
+++ b/cfg/windows.cfg
@@ -1310,6 +1310,26 @@
   <function name="KeBugCheckEx">
     <noreturn>true</noreturn>
   </function>
+  <!-- void CString::Format(LPCTSTR lpszFormat, ... ); -->
+  <function name="CString::Format">
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <formatstr/>
+    <arg nr="1">
+      <formatstr/>
+      <not-uninit/>
+    </arg>
+  </function>
+  <!-- void CString::AppendFormat(LPCTSTR lpszFormat, ... ); -->
+  <function name="CString::AppendFormat">
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <formatstr/>
+    <arg nr="1">
+      <formatstr/>
+      <not-uninit/>
+    </arg>
+  </function>
   <function name="printf_s">
     <noreturn>false</noreturn>
     <leak-ignore/>
diff --git a/lib/checkio.cpp b/lib/checkio.cpp
index e2d14850d..368e2277f 100644
--- a/lib/checkio.cpp
+++ b/lib/checkio.cpp
@@ -505,29 +505,16 @@ void CheckIO::checkWrongPrintfScanfArguments()
             bool scanf_s = false;
             int formatStringArgNo = -1;
 
-            if (tok->strAt(1) == "(" && _settings->library.formatstr_function(tok->str())) {
-                const std::map<int, Library::ArgumentChecks>& argumentChecks = _settings->library.argumentChecks.at(tok->str());
-                for (std::map<int, Library::ArgumentChecks>::const_iterator i = argumentChecks.cbegin(); i != argumentChecks.cend(); ++i) {
-                    if (i->second.formatstr) {
-                        formatStringArgNo = i->first - 1;
-                        break;
-                    }
-                }
-
-                scan = _settings->library.formatstr_scan(tok->str());
-                scanf_s = _settings->library.formatstr_secure(tok->str());
+            if (tok->strAt(1) == "(" && _settings->library.formatstr_function(tok)) {
+                formatStringArgNo = _settings->library.formatstr_argno(tok);
+                scan = _settings->library.formatstr_scan(tok);
+                scanf_s = _settings->library.formatstr_secure(tok);
             }
 
             if (formatStringArgNo >= 0) {
                 // formatstring found in library. Find format string and first argument belonging to format string.
                 if (!findFormat(static_cast<unsigned int>(formatStringArgNo), tok->tokAt(2), &formatStringTok, &argListTok))
                     continue;
-            } else if (isWindows && Token::Match(tok, "Format|AppendFormat (") &&
-                       Token::Match(tok->tokAt(-2), "%var% .") && tok->tokAt(-2)->variable() &&
-                       tok->tokAt(-2)->variable()->typeStartToken()->str() == "CString") {
-                // Find second parameter and format string
-                if (!findFormat(0, tok->tokAt(2), &formatStringTok, &argListTok))
-                    continue;
             } else if (Token::simpleMatch(tok, "swprintf (") && Token::Match(tok->tokAt(2)->nextArgument(), "%str%")) {
                 // Find third parameter and format string
                 if (!findFormat(1, tok->tokAt(2), &formatStringTok, &argListTok))
diff --git a/lib/library.cpp b/lib/library.cpp
index 711fe44a4..faa87a783 100644
--- a/lib/library.cpp
+++ b/lib/library.cpp
@@ -934,6 +934,33 @@ const Library::WarnInfo* Library::getWarnInfo(const Token* ftok) const
     return &i->second;
 }
 
+bool Library::formatstr_function(const Token* ftok) const
+{
+    return (!isNotLibraryFunction(ftok) &&
+            _formatstr.find(functionName(ftok)) != _formatstr.cend());
+}
+
+int Library::formatstr_argno(const Token* ftok) const
+{
+    const std::map<int, Library::ArgumentChecks>& argumentChecksFunc = argumentChecks.at(functionName(ftok));
+    for (std::map<int, Library::ArgumentChecks>::const_iterator i = argumentChecksFunc.cbegin(); i != argumentChecksFunc.cend(); ++i) {
+        if (i->second.formatstr) {
+            return i->first - 1;
+        }
+    }
+    return -1;
+}
+
+bool Library::formatstr_scan(const Token* ftok) const
+{
+    return _formatstr.at(functionName(ftok)).first;
+}
+
+bool Library::formatstr_secure(const Token* ftok) const
+{
+    return _formatstr.at(functionName(ftok)).second;
+}
+
 bool Library::isUseRetVal(const Token* ftok) const
 {
     return (!isNotLibraryFunction(ftok) &&
diff --git a/lib/library.h b/lib/library.h
index 02c965365..8607978e7 100644
--- a/lib/library.h
+++ b/lib/library.h
@@ -137,17 +137,13 @@ public:
         return ((func->groupId > 0) && ((func->groupId & 1) == 1));
     }
 
-    bool formatstr_function(const std::string& funcname) const {
-        return _formatstr.find(funcname) != _formatstr.cend();
-    }
+    bool formatstr_function(const Token* ftok) const;
 
-    bool formatstr_scan(const std::string& funcname) const {
-        return _formatstr.at(funcname).first;
-    }
+    int formatstr_argno(const Token* ftok) const;
 
-    bool formatstr_secure(const std::string& funcname) const {
-        return _formatstr.at(funcname).second;
-    }
+    bool formatstr_scan(const Token* ftok) const;
+
+    bool formatstr_secure(const Token* ftok) const;
 
     std::set<std::string> use;
     std::set<std::string> leakignore;
diff --git a/test/testio.cpp b/test/testio.cpp
index a683cb82c..6d24f7d7e 100644
--- a/test/testio.cpp
+++ b/test/testio.cpp
@@ -2474,9 +2474,11 @@ private:
               "    CString string;\n"
               "    string.Format(\"%I32d\", u32);\n"
               "    string.AppendFormat(\"%I32d\", u32);\n"
+              "    CString::Format(\"%I32d\", u32);\n"
               "}", false, false, Settings::Win32A);
         ASSERT_EQUALS("[test.cpp:4]: (warning) %I32d in format string (no. 1) requires '__int32' but the argument type is 'unsigned __int32 {aka unsigned int}'.\n"
-                      "[test.cpp:5]: (warning) %I32d in format string (no. 1) requires '__int32' but the argument type is 'unsigned __int32 {aka unsigned int}'.\n", errout.str());
+                      "[test.cpp:5]: (warning) %I32d in format string (no. 1) requires '__int32' but the argument type is 'unsigned __int32 {aka unsigned int}'.\n"
+                      "[test.cpp:6]: (warning) %I32d in format string (no. 1) requires '__int32' but the argument type is 'unsigned __int32 {aka unsigned int}'.\n", errout.str());
     }
 
     void testMicrosoftSecurePrintfArgument() {