diff --git a/lib/library.cpp b/lib/library.cpp
index f1058c7883a..d815b3ac615 100644
--- a/lib/library.cpp
+++ b/lib/library.cpp
@@ -1010,8 +1010,12 @@ std::string Library::getFunctionName(const Token *ftok) const
     if (ftok->astParent()) {
         bool error = false;
         const Token * tok = ftok->astParent()->isUnaryOp("&") ? ftok->astParent()->astOperand1() : ftok->next()->astOperand1();
-        const std::string ret = getFunctionName(tok, error);
-        return error ? std::string() : ret;
+        std::string ret = getFunctionName(tok, error);
+        if (error)
+            return {};
+        if (startsWith(ret, "::"))
+            ret.erase(0, 2);
+        return ret;
     }
 
     // Lookup function name without using AST..
diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 03b31da4bcc..70aa0ee17e8 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -9647,6 +9647,18 @@ void Tokenizer::simplifyBitfields()
     }
 }
 
+static bool isStdContainerOrIterator(const Token* tok, const Settings* settings)
+{
+    const Library::Container* ctr = settings->library.detectContainerOrIterator(tok, nullptr, /*withoutStd*/ true);
+    return ctr && startsWith(ctr->startPattern, "std ::");
+}
+
+static bool isStdSmartPointer(const Token* tok, const Settings* settings)
+{
+    const Library::SmartPointer* ptr = settings->library.detectSmartPointer(tok, /*withoutStd*/ true);
+    return ptr && startsWith(ptr->name, "std::");
+}
+
 // Add std:: in front of std classes, when using namespace std; was given
 void Tokenizer::simplifyNamespaceStd()
 {
@@ -9677,11 +9689,11 @@ void Tokenizer::simplifyNamespaceStd()
             if (userFunctions.find(tok->str()) == userFunctions.end() && mSettings->library.matchArguments(tok, "std::" + tok->str()))
                 insert = true;
         } else if (Token::simpleMatch(tok->next(), "<") &&
-                   (mSettings->library.detectContainerOrIterator(tok, nullptr, /*withoutStd*/ true) || mSettings->library.detectSmartPointer(tok, /*withoutStd*/ true)))
+                   (isStdContainerOrIterator(tok, mSettings) || isStdSmartPointer(tok, mSettings)))
             insert = true;
         else if (mSettings->library.hasAnyTypeCheck("std::" + tok->str()) ||
                  mSettings->library.podtype("std::" + tok->str()) ||
-                 mSettings->library.detectContainerOrIterator(tok, nullptr, /*withoutStd*/ true))
+                 isStdContainerOrIterator(tok, mSettings))
             insert = true;
 
         if (insert) {
diff --git a/test/cfg/qt.cpp b/test/cfg/qt.cpp
index 2bef064a983..2c45ba8340c 100644
--- a/test/cfg/qt.cpp
+++ b/test/cfg/qt.cpp
@@ -71,6 +71,16 @@ bool QString7(QString s, const QString& l) {
     return l.startsWith(s);
 }
 
+namespace NTestStd // #12355
+{
+    using namespace std;
+    QString QString_std(QString s)
+    {
+        s.replace("abc", "def");
+        return s;
+    }
+}
+
 void QByteArray1(QByteArray byteArrayArg)
 {
     for (int i = 0; i <= byteArrayArg.size(); ++i) {
diff --git a/test/cfg/std.cpp b/test/cfg/std.cpp
index 1d2c17e8de6..07f427e6fc1 100644
--- a/test/cfg/std.cpp
+++ b/test/cfg/std.cpp
@@ -4892,3 +4892,9 @@ void std_vector_data_arithmetic()
     buf.resize(1);
     memcpy(buf.data() + 0, "", 1);
 }
+
+std::string global_scope_std() // #12355
+{
+    ::std::stringstream ss;
+    return ss.str();
+}
\ No newline at end of file