diff --git a/cfg/posix.cfg b/cfg/posix.cfg
index cc8062add..c4106606d 100644
--- a/cfg/posix.cfg
+++ b/cfg/posix.cfg
@@ -28,7 +28,7 @@
 	  <leak-ignore/>
  </function>
   <function name="rename"> <noreturn>false</noreturn> <arg nr="1"><not-uninit/><not-null/></arg> <leak-ignore/> </function>
-  <function name="isatty"> <noreturn>false</noreturn> <arg nr="1"><not-uninit/><not-null/></arg> <leak-ignore/> </function>
+  <function name="isatty"> <noreturn>false</noreturn> <arg nr="1"><not-uninit/></arg> <leak-ignore/> </function>
   <resource>
     <dealloc>close</dealloc>
     <alloc init="true">open</alloc>
diff --git a/test/testnullpointer.cpp b/test/testnullpointer.cpp
index a60cb18bd..8f5f74716 100644
--- a/test/testnullpointer.cpp
+++ b/test/testnullpointer.cpp
@@ -88,6 +88,11 @@ private:
 
         // Test that std.cfg is configured correctly
         TEST_CASE(stdcfg);
+
+        // Load posix library file
+        LOAD_LIB_2(settings.library, "posix.cfg");
+        // Test that posix.cfg is configured correctly
+        TEST_CASE(posixcfg);
     }
 
     void check(const char code[], bool inconclusive = false, const char filename[] = "test.cpp", bool verify=true) {
@@ -2591,6 +2596,16 @@ private:
               "}\n");
         ASSERT_EQUALS("[test.cpp:2]: (error) Null pointer dereference\n", errout.str());
     }
+
+    void posixcfg() {
+        const char errp[] = "[test.cpp:1] -> [test.cpp:1]: (warning) Possible null pointer dereference: p - otherwise it is redundant to check it against null.\n";
+
+        check("void f(FILE *p){ isatty (*p);if(!p){}}");
+        ASSERT_EQUALS(errp,errout.str());
+
+        check("void f(){ isatty (0);}");
+        ASSERT_EQUALS("",errout.str());
+    }
 };
 
 REGISTER_TEST(TestNullPointer)