diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index e40d873cc..89bd6a3ee 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -640,11 +640,12 @@ SymbolDatabase::SymbolDatabase(const Tokenizer *tokenizer, const Settings *setti
                         tok = funcStart;
 
                         // class function
-                        if (tok->previous()->str() == "::")
+                        if (tok->previous() && tok->previous()->str() == "::")
                             addClassFunction(&scope, &tok, argStart);
 
                         // class destructor
-                        else if (tok->previous()->str() == "~" &&
+                        else if (tok->previous() &&
+                                 tok->previous()->str() == "~" &&
                                  tok->strAt(-2) == "::")
                             addClassFunction(&scope, &tok, argStart);
 
@@ -1100,6 +1101,17 @@ bool SymbolDatabase::isFunction(const Token *tok, const Scope* outerScope, const
         }
     }
 
+    // UNKNOWN_MACRO(a,b) { ... }
+    else if (outerScope->type == Scope::eGlobal &&
+             Token::Match(tok, "%var% (") &&
+             tok->isUpperCaseName() &&
+             Token::Match(tok->linkAt(1), ") {") &&
+             (!tok->previous() || Token::Match(tok->previous(), "[;{}]"))) {
+        *funcStart = tok;
+        *argStart = tok->next();
+        return true;
+    }
+
     // template constructor?
     else if (Token::Match(tok, "%var% <") && Token::simpleMatch(tok->next()->link(), "> (")) {
         const Token* tok2 = tok->next()->link()->next()->link();
diff --git a/test/testsymboldatabase.cpp b/test/testsymboldatabase.cpp
index 05560b273..75a03e1df 100644
--- a/test/testsymboldatabase.cpp
+++ b/test/testsymboldatabase.cpp
@@ -225,6 +225,8 @@ private:
 
         TEST_CASE(garbage);
 
+        TEST_CASE(isFunction); // UNKNOWN_MACRO(a,b) { .. }
+
         TEST_CASE(findFunction1);
         TEST_CASE(findFunction2); // mismatch: parameter passed by address => reference argument
 
@@ -1986,6 +1988,19 @@ private:
         }
     }
 
+    void isFunction() { // #5602 - UNKNOWN_MACRO(a,b) { .. }
+        GET_SYMBOL_DB("TEST(a,b) {\n"
+                      "  std::vector<int> messages;\n"
+                      "  foo(messages[2].size());\n"
+                      "}");
+        const Variable * const var = db ? db->getVariableFromVarId(1U) : nullptr;
+        ASSERT(db &&
+               db->findScopeByName("TEST") &&
+               var &&
+               var->typeStartToken() &&
+               var->typeStartToken()->str() == "std");
+    }
+
     void findFunction1() {
         GET_SYMBOL_DB("int foo(int x);\n" /* 1 */
                       "void foo();\n"     /* 2 */