diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index 37712f4c4..be9e65c69 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -745,6 +745,8 @@ SymbolDatabase::SymbolDatabase(const Tokenizer *tokenizer, const Settings *setti
                         // save function prototype in database
                         if (newFunc) {
                             Function* func = addGlobalFunctionDecl(scope, tok, argStart, funcStart);
+                            if (!func)
+                                break;
 
                             if (Token::Match(argStart->link(), ") const| noexcept")) {
                                 int arg = 2;
@@ -1658,6 +1660,9 @@ Function* SymbolDatabase::addGlobalFunction(Scope*& scope, const Token*& tok, co
     if (!function)
         function = addGlobalFunctionDecl(scope, tok, argStart, funcStart);
 
+    if (!function)
+        return 0;
+
     function->arg = argStart;
     function->token = funcStart;
     function->hasBody(true);
@@ -1683,6 +1688,8 @@ Function* SymbolDatabase::addGlobalFunctionDecl(Scope*& scope, const Token *tok,
     function.access = Public;
 
     // save the function name location
+    if (funcStart && isReservedName(funcStart->str()))
+        return 0;
     function.tokenDef = funcStart;
 
     function.isInline(false);
@@ -3588,3 +3595,28 @@ Function * SymbolDatabase::findFunctionInScope(const Token *func, const Scope *n
 
     return const_cast<Function *>(function);
 }
+
+//---------------------------------------------------------------------------
+
+bool SymbolDatabase::isReservedName(const std::string& iName) const
+{
+    static const std::set<std::string> c_keywords = make_container<std::set<std::string>>() <<
+        "auto" << "break" << "case" << "char" << "const" << "continue" << "default" << "do" <<
+        "double" << "else" << "enum" << "extern" << "float" << "for" << "goto" << "if" << "inline" <<
+        "int" << "long" << "register" << "restrict" << "return" << "short" << "signed" << "sizeof" <<
+        "static" << "struct" << "switch" << "typedef" << "union" << "unsigned" << "void" << "volatile" <<
+        "while";
+    static const std::set<std::string> cpp_keywords = make_container<std::set<std::string>>() <<
+        "alignas" << "alignof" << "and" << "and_eq" << "asm" << "auto" << "bitand" << "bitor" << "bool" <<
+         "break" << "case" << "catch" << "char" << "char16_t" << "char32_t" << "class" << "compl" <<
+         "concept" << "const" << "constexpr" << "const_cast" << "continue" << "decltype" << "default" <<
+         "delete" << "do" << "double" << "dynamic_cast" << "else" << "enum" << "explicit" << "export" <<
+         "extern" << "false" << "float" << "for" << "friend" << "goto" << "if" << "inline" << "int" << "long" <<
+         "mutable" << "namespace" << "new" << "noexcept" << "not" << "not_eq" << "nullptr" << "operator" <<
+         "or" << "or_eq" << "private" << "protected" << "public" << "register" << "reinterpret_cast" <<
+         "requires" << "return" << "short" << "signed" << "sizeof" << "static" << "static_assert" <<
+         "static_cast" << "struct" << "switch" << "template" << "this" << "thread_local" << "throw" <<
+         "true" << "try" << "typedef" << "typeid" << "typename" << "union" << "unsigned" << "using" <<
+         "virtual" << "void" << "volatile" << "wchar_t" << "while" << "xor" << "xor_eq";
+    return (c_keywords.find(iName) != c_keywords.cend()) || (isCPP() && (cpp_keywords.find(iName) != cpp_keywords.cend()));
+}
diff --git a/lib/symboldatabase.h b/lib/symboldatabase.h
index 3fd02e2f9..c936684ec 100644
--- a/lib/symboldatabase.h
+++ b/lib/symboldatabase.h
@@ -1005,6 +1005,9 @@ private:
     const Scope *findNamespace(const Token * tok, const Scope * scope) const;
     Function *findFunctionInScope(const Token *func, const Scope *ns);
 
+    /** Whether iName is a keyword as defined in http://en.cppreference.com/w/c/keyword and http://en.cppreference.com/w/cpp/keyword*/
+    bool isReservedName(const std::string& iName) const;
+
 
     const Tokenizer *_tokenizer;
     const Settings *_settings;
diff --git a/test/testgarbage.cpp b/test/testgarbage.cpp
index d5868f6b4..5239dbe94 100644
--- a/test/testgarbage.cpp
+++ b/test/testgarbage.cpp
@@ -78,6 +78,8 @@ private:
         TEST_CASE(garbageCode37); // #5166
         TEST_CASE(garbageCode38); // #6666
         TEST_CASE(garbageCode39); // #6686
+        TEST_CASE(garbageCode40); // #6620
+        TEST_CASE(garbageCode41); // #6685
 
         TEST_CASE(garbageValueFlow);
         TEST_CASE(garbageSymbolDatabase);
@@ -455,6 +457,14 @@ private:
         checkCode("({ (); strcat(strcat(() ()) ()) })");
     }
 
+    void garbageCode40() { // #6620
+        ASSERT_THROW(checkCode("{ ( ) () { virtual } ; { } E } A { : { } ( ) } * const ( ) const { }"), InternalError);
+    }
+
+    void garbageCode41() { // #6685
+        ASSERT_THROW(checkCode(" { } { return } *malloc(__SIZE_TYPE__ size); *memcpy(void n); static * const () { memcpy (*slot, 3); } { (); } { }"), InternalError);
+    }
+
     void garbageValueFlow() {
         // #6089
         const char* code = "{} int foo(struct, x1, struct x2, x3, int, x5, x6, x7)\n"
diff --git a/test/testsimplifytokens.cpp b/test/testsimplifytokens.cpp
index b55aa696f..e56792770 100644
--- a/test/testsimplifytokens.cpp
+++ b/test/testsimplifytokens.cpp
@@ -805,7 +805,7 @@ private:
         ASSERT_EQUALS("\n\n##file 0\n1: else { if ( ab ) { cd } else { ef } } gh\n", elseif(code));
 
         // syntax error: assert there is no segmentation fault
-        ASSERT_EQUALS("\n\n##file 0\n1: else if ( x ) { }\n", elseif("else if (x) { }"));
+        ASSERT_THROW(elseif("else if (x) { }"), InternalError);
 
         {
             const char src[] =  "void f(int g,int f) {\n"
diff --git a/test/testsymboldatabase.cpp b/test/testsymboldatabase.cpp
index d5ad4a01b..86e533989 100644
--- a/test/testsymboldatabase.cpp
+++ b/test/testsymboldatabase.cpp
@@ -1919,8 +1919,7 @@ private:
     }
 
     void symboldatabase36() { // ticket #4892
-        check("void struct ( ) { if ( 1 ) } int main ( ) { }");
-        ASSERT_EQUALS("", errout.str());
+        ASSERT_THROW(check("void struct ( ) { if ( 1 ) } int main ( ) { }"), InternalError);
     }
 
     void symboldatabase37() {
diff --git a/test/testtokenize.cpp b/test/testtokenize.cpp
index a22296861..c1f618fc3 100644
--- a/test/testtokenize.cpp
+++ b/test/testtokenize.cpp
@@ -1270,7 +1270,7 @@ private:
 
     void ifAddBraces15() {
         // ticket #2616 - unknown macro before if
-        ASSERT_EQUALS("{ A if ( x ) { y ( ) ; } }", tokenizeAndStringify("{A if(x)y();}", false));
+        ASSERT_THROW(tokenizeAndStringify("{A if(x)y();}", false), InternalError);
     }
 
     void ifAddBraces16() { // ticket # 2739 (segmentation fault)
@@ -6145,7 +6145,7 @@ private:
                                "operator ( ) ; "
                                "}";
 
-        ASSERT_EQUALS(result, tokenizeAndStringify(code,false));
+        ASSERT_EQUALS(result, tokenizeAndStringify(code, /*simplify=*/false, /*expand=*/true, /*platform=*/Settings::Unspecified, "test.c"));
     }
 
     void simplifyOperatorName2() {