diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index 9281b54a3..8935e5073 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -1997,7 +1997,7 @@ bool SymbolDatabase::isFunction(const Token *tok, const Scope* outerScope, const
              Token::simpleMatch(tok->linkAt(1), ") {") &&
              (!tok->previous() || Token::Match(tok->previous(), ";|}"))) {
         if (mTokenizer.isC()) {
-            debugMessage(tok, "debug", "SymbolDatabase::isFunction found C function '" + tok->str() + "' without a return type.");
+            returnImplicitIntError(tok);
             *funcStart = tok;
             *argStart = tok->next();
             *declEnd = tok->linkAt(1)->next();
@@ -3522,6 +3522,19 @@ void SymbolDatabase::debugMessage(const Token *tok, const std::string &type, con
     }
 }
 
+void SymbolDatabase::returnImplicitIntError(const Token *tok) const
+{
+    if (tok && mSettings.severity.isEnabled(Severity::portability) && mSettings.standards.c != Standards::C89 && mErrorLogger) {
+        const std::list<const Token*> locationList(1, tok);
+        const ErrorMessage errmsg(locationList, &mTokenizer.list,
+                                  Severity::portability,
+                                  "returnImplicitInt",
+                                  "Omitted return type of function '" + tok->str() + "' defaults to int, this is not supported by ISO C99 and later standards.",
+                                  Certainty::normal);
+        mErrorLogger->reportErr(errmsg);
+    }
+}
+
 const Function* Type::getFunction(const std::string& funcName) const
 {
     if (classScope) {
diff --git a/lib/symboldatabase.h b/lib/symboldatabase.h
index a235527df..f9f4039ff 100644
--- a/lib/symboldatabase.h
+++ b/lib/symboldatabase.h
@@ -1371,6 +1371,8 @@ public:
      */
     void debugMessage(const Token *tok, const std::string &type, const std::string &msg) const;
 
+    void returnImplicitIntError(const Token *tok) const;
+
     void printOut(const char * title = nullptr) const;
     void printVariable(const Variable *var, const char *indent) const;
     void printXml(std::ostream &out) const;
diff --git a/test/testsymboldatabase.cpp b/test/testsymboldatabase.cpp
index 06d4d1915..cf92cb27c 100644
--- a/test/testsymboldatabase.cpp
+++ b/test/testsymboldatabase.cpp
@@ -2380,12 +2380,12 @@ private:
     }
 
 #define check(...) check_(__FILE__, __LINE__, __VA_ARGS__)
-    void check_(const char* file, int line, const char code[], bool debug = true, const char filename[] = "test.cpp") {
+    void check_(const char* file, int line, const char code[], bool debug = true, const char filename[] = "test.cpp", const Settings* pSettings = nullptr) {
         // Clear the error log
         errout.str("");
 
         // Check..
-        const Settings settings = settingsBuilder(settings1).debugwarnings(debug).build();
+        const Settings settings = settingsBuilder(pSettings ? *pSettings : settings1).debugwarnings(debug).build();
 
         // Tokenize..
         Tokenizer tokenizer(&settings, this);
@@ -2986,7 +2986,12 @@ private:
         ASSERT_EQUALS("", errout.str());
 
         check("main(int argc, char *argv[]) { }", true, "test.c");
-        ASSERT_EQUALS("[test.c:1]: (debug) SymbolDatabase::isFunction found C function 'main' without a return type.\n", errout.str());
+        ASSERT_EQUALS("", errout.str());
+
+        const Settings s = settingsBuilder(settings1).severity(Severity::portability).build();
+        check("main(int argc, char *argv[]) { }", false, "test.c", &s);
+        ASSERT_EQUALS("[test.c:1]: (portability) Omitted return type of function 'main' defaults to int, this is not supported by ISO C99 and later standards.\n",
+                      errout.str());
 
         check("namespace boost {\n"
               "    std::locale generate_locale()\n"