diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 5b63400d226..d1058b496e2 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -1072,7 +1072,8 @@ void Tokenizer::simplifyTypedef()
 
         if (indentlevel == 0 && tok->str() == "typedef") {
             TypedefSimplifier ts(tok);
-            if (!ts.fail() && numberOfTypedefs[ts.name()] == 1) {
+            if (!ts.fail() && numberOfTypedefs[ts.name()] == 1 &&
+                (numberOfTypedefs.find(ts.getTypedefToken()->strAt(1)) == numberOfTypedefs.end() || ts.getTypedefToken()->strAt(2) == "(")) {
                 if (mSettings.severity.isEnabled(Severity::portability) && ts.isInvalidConstFunctionType(typedefs))
                     reportError(tok->next(), Severity::portability, "invalidConstFunctionType",
                                 "It is unspecified behavior to const qualify a function type.");
diff --git a/test/testsimplifytypedef.cpp b/test/testsimplifytypedef.cpp
index c21ab199e0c..7d1a59e1a89 100644
--- a/test/testsimplifytypedef.cpp
+++ b/test/testsimplifytypedef.cpp
@@ -216,6 +216,7 @@ class TestSimplifyTypedef : public TestFixture {
         TEST_CASE(simplifyTypedef150);
         TEST_CASE(simplifyTypedef151);
         TEST_CASE(simplifyTypedef152);
+        TEST_CASE(simplifyTypedef153);
 
         TEST_CASE(simplifyTypedefFunction1);
         TEST_CASE(simplifyTypedefFunction2); // ticket #1685
@@ -1226,7 +1227,7 @@ class TestSimplifyTypedef : public TestFixture {
                             "LPCSTR ccp;";
 
         const char expected[] =
-            "char c ; "
+            "; char c ; "
             "char * cp ; "
             "const char * ccp ;";
 
@@ -3563,6 +3564,16 @@ class TestSimplifyTypedef : public TestFixture {
         ASSERT_EQUALS(exp, tok(code));
     }
 
+    void simplifyTypedef153() {
+        const char* code{}, *exp{}; // #12647
+        code = "typedef unsigned long X;\n"
+               "typedef unsigned long X;\n"
+               "typedef X Y;\n"
+               "Y y;\n";
+        exp = "long y ;";
+        ASSERT_EQUALS(exp, tok(code));
+    }
+
     void simplifyTypedefFunction1() {
         {
             const char code[] = "typedef void (*my_func)();\n"