diff --git a/lib/comp.c b/lib/comp.c
index 2a7728e..2cb4f13 100644
--- a/lib/comp.c
+++ b/lib/comp.c
@@ -295,14 +295,15 @@ static void fini_class_level_variable_buffer (hcl_t* hcl, hcl_oocsc_t* dst)
 	}
 }
 
-static int add_class_level_variable (hcl_t* hcl, hcl_oocsc_t* dst, const hcl_cnode_t* var, const hcl_bch_t* desc)
+static int add_class_level_variable (hcl_t* hcl, hcl_oocsc_t* dst, hcl_oocsc_t* altdst, const hcl_cnode_t* var, const hcl_bch_t* desc)
 {
 	/* it downcasts hcl_oocsc_t* to hcl_oocs_t*. take extra care to keep their type defintion
 	 * compatible for downcasting in hcl-cmn.h */
 	hcl_oocs_t* name;
 
 	name = HCL_CNODE_GET_TOK(var);
-	if (__find_word_in_string((hcl_oocs_t*)dst, name, 0, HCL_NULL) >= 0)
+	if (__find_word_in_string((hcl_oocs_t*)dst, name, 0, HCL_NULL) >= 0 ||
+	   (__find_word_in_string((hcl_oocs_t*)altdst, name, 0, HCL_NULL) >= 0))
 	{
 		hcl_setsynerrbfmt (
 			hcl, HCL_SYNERR_VARNAMEDUP, HCL_CNODE_GET_LOC(var), HCL_NULL,
@@ -3801,7 +3802,7 @@ static int compile_var (hcl_t* hcl, hcl_cnode_t* src)
 					goto oops;
 				}
 
-				if (add_class_level_variable(hcl, &cbi->ivars, tmp, "instance") <= -1) goto oops;
+				if (add_class_level_variable(hcl, &cbi->ivars, &cbi->cvars, tmp, "instance") <= -1) goto oops;
 				cbi->nivars++;
 			}
 			else
@@ -3815,7 +3816,7 @@ static int compile_var (hcl_t* hcl, hcl_cnode_t* src)
 					goto oops;
 				}
 
-				if (add_class_level_variable(hcl, &cbi->cvars, tmp, "class") <= -1) goto oops;
+				if (add_class_level_variable(hcl, &cbi->cvars, &cbi->ivars, tmp, "class") <= -1) goto oops;
 				cbi->ncvars++;
 			}
 
diff --git a/t/class-5001.err b/t/class-5001.err
index 1dff216..c09da1e 100644
--- a/t/class-5001.err
+++ b/t/class-5001.err
@@ -289,11 +289,14 @@ class Kuduro [a b c] {
 }
 
 ---
-class Kuduru [a [b] c] {
+
+class Kuduro [a [b] c] {
 	var d e
-	var b    ##TODO: should this be prohibited?
+	var b ##ERROR: syntax error - duplicate instance variable name 'b'
 }
 
+---
+
 class Kuduro [a [b] c] {
 	var d e
 	var(#class) b ##ERROR: syntax error - duplicate class variable name 'b'