diff --git a/lib/checkother.cpp b/lib/checkother.cpp
index 67366d70b..62b44b31a 100644
--- a/lib/checkother.cpp
+++ b/lib/checkother.cpp
@@ -3176,7 +3176,8 @@ void CheckOther::checkDuplicateExpression()
             if (Token::Match(tok, ",|=|return|(|&&|%oror% %var% %comp%|- %var% )|&&|%oror%|;|,") &&
                 tok->strAt(1) == tok->strAt(3)) {
                 // float == float and float != float are valid NaN checks
-                if (Token::Match(tok->tokAt(2), "==|!=") && tok->next()->varId()) {
+                // float - float is a valid Inf check
+                if (Token::Match(tok->tokAt(2), "==|!=|-") && tok->next()->varId()) {
                     const Variable * var = symbolDatabase->getVariableFromVarId(tok->next()->varId());
                     if (var && var->typeStartToken() == var->typeEndToken()) {
                         if (Token::Match(var->typeStartToken(), "float|double"))
diff --git a/test/testother.cpp b/test/testother.cpp
index b766bf05a..1462e6dd2 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -5181,8 +5181,8 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
-    void duplicateExpression2() { // ticket #2730
-        check("int main()\n"
+    void duplicateExpression2() { // check if float is NaN or Inf
+        check("int main()\n" // ticket #2730
               "{\n"
               "    long double ldbl;\n"
               "    double dbl, in;\n"
@@ -5199,6 +5199,9 @@ private:
         ASSERT_EQUALS("[test.cpp:7]: (error) Passing value -1.0 to sqrtl() leads to undefined result.\n"
                       "[test.cpp:8]: (error) Passing value -1.0 to sqrt() leads to undefined result.\n"
                       "[test.cpp:9]: (error) Passing value -1.0 to sqrtf() leads to undefined result.\n", errout.str());
+
+        check("float f(float x) { return x-x; }"); // ticket #4485 (Inf)
+        ASSERT_EQUALS("", errout.str());
     }
 
     void duplicateExpression3() {