diff --git a/lib/checktype.cpp b/lib/checktype.cpp
index c9c9179f0..2faa922e5 100644
--- a/lib/checktype.cpp
+++ b/lib/checktype.cpp
@@ -238,7 +238,8 @@ void CheckType::checkSignConversion()
 
             // Check if there are signed operands that can be negative..
             std::stack<const Token *> tokens;
-            tokens.push(tok);
+            tokens.push(tok->astOperand1());
+            tokens.push(tok->astOperand2());
             while (!tokens.empty()) {
                 const Token *tok1 = tokens.top();
                 tokens.pop();
@@ -268,8 +269,6 @@ void CheckType::checkSignConversion()
                         break;
                     }
                 }
-                tokens.push(tok1->astOperand1());
-                tokens.push(tok1->astOperand2());
             }
         }
     }
diff --git a/test/testtype.cpp b/test/testtype.cpp
index 31d27017c..b36b780b3 100644
--- a/test/testtype.cpp
+++ b/test/testtype.cpp
@@ -117,6 +117,12 @@ private:
               "void f2() { f1(-4); }");
         ASSERT_EQUALS("[test.cpp:1]: (warning) Suspicious code: sign conversion of x in calculation, even though x can have a negative value\n", errout.str());
 
+        check("unsigned int f1(int x) {" // #6168: FP for inner calculation
+              "  return 5U * (1234 - x);\n" // <- signed subtraction, x is not sign converted
+              "}\n"
+              "void f2() { f1(-4); }");
+        ASSERT_EQUALS("", errout.str());
+
         // Dont warn for + and -
         check("void f1(int x) {"
               "  a = x + 5U;\n"