diff --git a/lib/checkfunctions.cpp b/lib/checkfunctions.cpp
index b65f3eb76..ef80d237b 100644
--- a/lib/checkfunctions.cpp
+++ b/lib/checkfunctions.cpp
@@ -125,7 +125,7 @@ void CheckFunctions::invalidFunctionUsage()
                     else if (!mSettings->library.isIntArgValid(functionToken, argnr, 1))
                         invalidFunctionArgError(argtok, functionToken->str(), argnr, nullptr, mSettings->library.validarg(functionToken, argnr));
                 }
-// check <strz>
+                // check <strz>
                 if (mSettings->library.isargstrz(functionToken, argnr)) {
                     if (Token::Match(argtok, "& %var% !![") && argtok->next() && argtok->next()->valueType()) {
                         const ValueType * valueType = argtok->next()->valueType();
@@ -151,13 +151,17 @@ void CheckFunctions::invalidFunctionUsage()
                         if (Token::simpleMatch(varTok, "= {")) {
                             varTok = varTok->tokAt(1);
                             auto charsUntilFirstZero = 0;
-                            while (varTok && !Token::simpleMatch(varTok->next(), "}")) {
-                                if (!Token::simpleMatch(varTok->next(), ",")) {
-                                    ++charsUntilFirstZero;
-                                }
+                            bool search = true;
+                            while (search && varTok && !Token::simpleMatch(varTok->next(), "}")) {
                                 varTok = varTok->next();
-                                if (varTok && varTok->hasKnownIntValue() && varTok->getKnownIntValue() == 0) {
-                                    break; // stop counting for cases like char buf[3] = {'x', '\0', 'y'};
+                                if (!Token::simpleMatch(varTok, ",")) {
+                                    if (Token::Match(varTok, "%op%")) {
+                                        varTok = varTok->next();
+                                        continue;
+                                    }
+                                    ++charsUntilFirstZero;
+                                    if (varTok && varTok->hasKnownIntValue() && varTok->getKnownIntValue() == 0)
+                                        search=false; // stop counting for cases like char buf[3] = {'x', '\0', 'y'};
                                 }
                             }
                             if (varTok && varTok->hasKnownIntValue() && varTok->getKnownIntValue() != 0
diff --git a/test/testfunctions.cpp b/test/testfunctions.cpp
index ec24780f8..eb2285df7 100644
--- a/test/testfunctions.cpp
+++ b/test/testfunctions.cpp
@@ -650,6 +650,24 @@ private:
               "}");
         ASSERT_EQUALS("", errout.str());
 
+        check("FILE* f(void) {\n"
+              "  const char fileName[] = { \'0\' + 42 };\n" // no size is explicitly defined, no implicit '\0' is added
+              "  return fopen(fileName, \"r\"); \n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:3]: (error) Invalid fopen() argument nr 1. A nul-terminated string is required.\n", errout.str());
+
+        check("FILE* f(void) {\n"
+              "  const char fileName[] = { \'0\' + 42, \'x\' };\n" // no size is explicitly defined, no implicit '\0' is added
+              "  return fopen(fileName, \"r\"); \n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:3]: (error) Invalid fopen() argument nr 1. A nul-terminated string is required.\n", errout.str());
+
+        check("FILE* f(void) {\n"
+              "  const char fileName[2] = { \'0\' + 42 };\n" // implicitly '\0' added at the end because size is set to 2
+              "  return fopen(fileName, \"r\"); \n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
         check("FILE* f(void) {\n"
               "  const char fileName[] = { };\n"
               "  return fopen(fileName, \"r\"); \n"