diff --git a/lib/checkclass.cpp b/lib/checkclass.cpp
index fc7f6a448..a45f918a3 100644
--- a/lib/checkclass.cpp
+++ b/lib/checkclass.cpp
@@ -184,6 +184,13 @@ void CheckClass::createSymbolDatabase()
                             break;
                         }
 
+                        // friend function
+                        else if (tok1->previous()->str() == "friend")
+                        {
+                            function.isFriend = true;
+                            break;
+                        }
+
                         tok1 = tok1->previous();
                     }
 
@@ -1867,7 +1874,7 @@ void CheckClass::checkConst()
             const Func & func = *it1;
 
             // does the function have a body?
-            if (func.type == Func::Function && func.hasBody && !func.isStatic && !func.isConst && !func.isVirtual)
+            if (func.type == Func::Function && func.hasBody && !func.isFriend && !func.isStatic && !func.isConst && !func.isVirtual)
             {
                 // get function name
                 const std::string functionName((func.tokenDef->isName() ? "" : "operator") + func.tokenDef->str());
diff --git a/lib/checkclass.h b/lib/checkclass.h
index 6bc4ddc0b..db47e5830 100644
--- a/lib/checkclass.h
+++ b/lib/checkclass.h
@@ -181,6 +181,7 @@ private:
               isConst(false),
               isVirtual(false),
               isStatic(false),
+              isFriend(false),
               isOperator(false),
               type(Function)
         {
@@ -194,6 +195,7 @@ private:
         bool isConst;          // is const
         bool isVirtual;        // is virtual
         bool isStatic;         // is static
+        bool isFriend;         // is friend
         bool isOperator;       // is operator
         Type type;             // constructor, destructor, ...
     };
diff --git a/test/testclass.cpp b/test/testclass.cpp
index f133cc6cf..252c032e1 100644
--- a/test/testclass.cpp
+++ b/test/testclass.cpp
@@ -141,6 +141,7 @@ private:
         TEST_CASE(constFunc); // a function that calls const functions can be const
         TEST_CASE(constVirtualFunc);
         TEST_CASE(constIfCfg);  // ticket #1881 - fp when there are #if
+        TEST_CASE(constFriend); // ticket #1921 - fp for friend function
     }
 
     // Check the operator Equal
@@ -3870,6 +3871,15 @@ private:
         checkConst(code, &settings);
         ASSERT_EQUALS("", errout.str());
     }
+
+    void constFriend()	// ticket #1921
+    {
+        const char code[] = "class foo {\n"
+                            "    friend void f() { }\n"
+                            "};";
+        checkConst(code);
+        ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestClass)