diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index bbc02b320..337e1cdb0 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -9446,6 +9446,11 @@ void Tokenizer::simplifyOperatorName()
                 if (par && par->isName()) {
                     op += par->str();
                     par = par->next();
+                    // merge namespaces eg. 'operator std :: string () const {'
+                    if (par && par->str() == "::" && par->next() && par->next()->isName()) {
+                        op += par->str();
+                        par = par->next();
+                    }
                     done = false;
                 }
                 if (Token::Match(par, "=|.|++|--|%op%")) {
diff --git a/test/testsimplifytokens.cpp b/test/testsimplifytokens.cpp
index 1413d75c8..6c73ebf67 100644
--- a/test/testsimplifytokens.cpp
+++ b/test/testsimplifytokens.cpp
@@ -294,6 +294,8 @@ private:
         TEST_CASE(simplifyTypedefFunction7);
         TEST_CASE(simplifyTypedefFunction8);
 
+        TEST_CASE(simplifyOperator1);
+
         TEST_CASE(reverseArraySyntax)
         TEST_CASE(simplify_numeric_condition)
         TEST_CASE(simplify_condition);
@@ -6168,6 +6170,21 @@ private:
         ASSERT_EQUALS("", errout.str());  // make sure that there is no internal error
     }
 
+    void simplifyOperator1() {
+        // #3237 - error merging namespaces with operators
+        const char code[] = "class c {\n"
+                            "public:\n"
+                            "    operator std::string() const;\n"
+                            "    operator string() const;\n"
+                            "};\n";
+        const char expected[] = "class c { "
+                                "public: "
+                                "operatorstd::string ( ) const ; "
+                                "operatorstring ( ) const ; "
+                                "} ;";
+        ASSERT_EQUALS(expected, tok(code));
+    }
+
     void reverseArraySyntax() {
         ASSERT_EQUALS("a [ 13 ]", tok("13[a]"));
     }