diff --git a/compiler/ninl.pas b/compiler/ninl.pas
index 616f108511..a44bb76e09 100644
--- a/compiler/ninl.pas
+++ b/compiler/ninl.pas
@@ -4179,7 +4179,9 @@ implementation
             end;
 
           in_slice_x:
-            internalerror(2005101502);
+            { slice can be used only in calls for open array parameters, so it has to be converted appropriatly before
+              if we get here, the array could not be passed to an open array parameter so it is an error }
+            CGMessagePos(left.fileinfo,type_e_mismatch);
 
           in_ord_x,
           in_chr_byte:
diff --git a/tests/webtbf/tw39806.pp b/tests/webtbf/tw39806.pp
new file mode 100644
index 0000000000..a5067ac44e
--- /dev/null
+++ b/tests/webtbf/tw39806.pp
@@ -0,0 +1,18 @@
+{ %fail }
+program test;
+
+type
+  TByteDynArr = array of byte;
+
+procedure proc(a: TByteDynArr);
+begin
+  Writeln(Length(a));
+end;
+
+var
+  x: array of byte;
+begin
+  x:= [1,2,3,4];
+  proc(Slice(x, 2));
+  // <source>(15,19) Fatal: Internal error 2005101501
+end.