diff --git a/cfg/std.cfg b/cfg/std.cfg
index c1ba3c546..d199c514b 100644
--- a/cfg/std.cfg
+++ b/cfg/std.cfg
@@ -197,14 +197,12 @@
   <function name="mbstowcs">
         <noreturn>false</noreturn>
         <leak-ignore/>
-        <arg nr="1"><not-uninit/></arg>
         <arg nr="2"><not-null/><not-uninit/></arg>
         <arg nr="3"><not-uninit/></arg>
   </function>
   <function name="wcstombs">
         <noreturn>false</noreturn>
         <leak-ignore/>
-        <arg nr="1"><not-uninit/></arg>
         <arg nr="2"><not-null/><not-uninit/></arg>
         <arg nr="3"><not-uninit/></arg>
   </function>
diff --git a/test/testuninitvar.cpp b/test/testuninitvar.cpp
index 0d1b94a27..7be3831e4 100644
--- a/test/testuninitvar.cpp
+++ b/test/testuninitvar.cpp
@@ -3711,6 +3711,18 @@ private:
                        "  putchar (*c);\n"
                        "}");
         ASSERT_EQUALS("", errout.str());
+
+        // #6116 False positive uninitvar - first argument to wcstombs()
+        checkUninitVar("void f( wchar_t *wstr) {\n"
+                       "  char buf[10];\n"
+                       "  wcstombs (buf, wstr, 3);\n"
+                       "}");
+        ASSERT_EQUALS("", errout.str());
+        checkUninitVar("void f( char *str) {\n"
+                       "  wchar_t wbuf[10];\n"
+                       "  mbstowcs (wbuf, str, 3);\n"
+                       "}");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void checkDeadPointer(const char code[]) {