diff --git a/moo/kernel/Class.moo b/moo/kernel/Class.moo
index 675652f..ad1b115 100644
--- a/moo/kernel/Class.moo
+++ b/moo/kernel/Class.moo
@@ -10,9 +10,9 @@ interface ClassInterface
 //
 class(#pointer,#limited,#uncopyable) Class(Apex) [ClassInterface]
 {
-	var spec, selfspec, superclass, subclasses, name, modname.
+	var name, instmthdic, classmthdic, nsup, nsdic.
+	var spec, selfspec, superclass, subclasses, modname.
 	var instvars, classinstvars, classvars, pooldics.
-	var instmthdic, classmthdic, nsup, nsdic.
 	var trsize, trgc, initv, initv_ci.
 
 	method(#class) initialize { ^self }
@@ -46,6 +46,5 @@ class(#pointer,#limited,#uncopyable) Class(Apex) [ClassInterface]
 
 class(#pointer,#limited,#uncopyable) Interface(Apex)
 {
-	var name.
-	var instmthdic, classmthdic, nsup, nsdic.
+	var name, instmthdic, classmthdic, nsup, nsdic.
 }
diff --git a/moo/lib/comp.c b/moo/lib/comp.c
index f16c514..829295f 100644
--- a/moo/lib/comp.c
+++ b/moo/lib/comp.c
@@ -9079,17 +9079,29 @@ static int ciim_on_each_method (moo_t* moo, moo_oop_dic_t dic, moo_oop_associati
 	mth = moo_findmethodinclasschain(moo, ciim->_class, ciim->mth_type, &name);
 	if (!mth)
 	{
-		/* TODO: take methods from interface..*/
 		if (MOO_CLASSOF(moo, ass->value) == moo->_method)
 		{
+			moo_oow_t i;
+			moo_oop_method_t im;
+
 			mth = (moo_oop_method_t)ass->value;
-#if 0
-			if (!moo_putatdic(moo, ciim->_class->mthdic[ciim->mth_type], (moo_oop_t)mth->name, (moo_oop_t)mth))
+			for (i = 0; i < ciim->cc->ifce_mths[ciim->mth_type].count; i++)
 			{
-/* TODO: error handling. GC safety, etc */
- 			}
-#else
-			/* TODO: check duplication */
+				im = (moo_oop_method_t)ciim->cc->ifce_mths[ciim->mth_type].ptr[i];
+				if (mth->name == im->name)
+				{
+					/* duplicate interface method name found */
+					moo_setsynerrbfmt (moo, MOO_SYNERR_MTHNAMEDUPL, MOO_NULL, MOO_NULL,
+						"%.*js defined in multiple interfaces for %.*js - %.*js, %.*js", 
+						name.len, name.ptr,
+						MOO_OBJ_GET_SIZE(ciim->_class->name), MOO_OBJ_GET_CHAR_SLOT(ciim->_class->name),
+						MOO_OBJ_GET_SIZE(im->owner->name), MOO_OBJ_GET_CHAR_SLOT(im->owner->name),
+						MOO_OBJ_GET_SIZE(ciim->ifce->name), MOO_OBJ_GET_CHAR_SLOT(ciim->ifce->name)
+					);
+					return -1;
+				}
+			}
+
 			if (add_oop_to_oopbuf(moo, &ciim->cc->ifce_mths[ciim->mth_type], (moo_oop_t)mth) <= -1)
 			{
 				const moo_ooch_t* oldmsg = moo_backuperrmsg(moo);
@@ -9101,8 +9113,7 @@ static int ciim_on_each_method (moo_t* moo, moo_oop_dic_t dic, moo_oop_associati
 				);
 				return -1;
 			}
-#endif
-		
+
 			return 0;
 		}
 
@@ -9213,6 +9224,7 @@ static int check_class_interface_conformance (moo_t* moo)
 		if (!class_implements_interface(moo, cc->self_oop, (moo_oop_interface_t)cc->ifces.ptr[i])) return -1;
 	}
 
+	MOO_STATIC_ASSERT (MOO_METHOD_INSTANCE == 0 && MOO_METHOD_CLASS == 1);
 	for (j = MOO_METHOD_INSTANCE; j <= MOO_METHOD_CLASS; j++)
 	{
 		for (i = 0; i < cc->ifce_mths[j].count; i++)
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index b30db19..6b30c6a 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -1847,8 +1847,8 @@ moo_oop_method_t moo_findmethod (moo_t* moo, moo_oop_t receiver, moo_oop_char_t
 
 	if (in_super) 
 	{
-		MOO_ASSERT (moo, moo->active_method);
-		MOO_ASSERT (moo, moo->active_method->owner);
+		MOO_ASSERT (moo, moo->active_method != MOO_NULL);
+		MOO_ASSERT (moo, moo->active_method->owner != MOO_NULL);
 
 		/* if 'super' is allowed in the interface method, the owner field
 		 * can be an interface. super must not be allowed  in the interface
diff --git a/moo/lib/moo.c b/moo/lib/moo.c
index 7bad723..aaa5fc7 100644
--- a/moo/lib/moo.c
+++ b/moo/lib/moo.c
@@ -873,8 +873,8 @@ int moo_genpfmethod (moo_t* moo, moo_mod_t* mod, moo_oop_class_t _class, moo_met
 	mth->literal_frame[0] = (moo_oop_t)pfidsym;
 
 	/* premable should contain the index to the literal frame which is always 0 */
-	mth->owner = _class;
-	mth->name = mnsym;
+	MOO_STORE_OOP (moo, (moo_oop_t*)&mth->owner, (moo_oop_t)_class);
+	MOO_STORE_OOP (moo, (moo_oop_t*)&mth->name, (moo_oop_t)mnsym);
 	if (variadic) preamble_flags |= MOO_METHOD_PREAMBLE_FLAG_VARIADIC;
 	mth->preamble = MOO_SMOOI_TO_OOP(MOO_METHOD_MAKE_PREAMBLE(MOO_METHOD_PREAMBLE_NAMED_PRIMITIVE, 0, preamble_flags));
 	mth->preamble_data[0] = MOO_SMPTR_TO_OOP(0);
diff --git a/moo/lib/moo.h b/moo/lib/moo.h
index cd9d1d1..6d0a5db 100644
--- a/moo/lib/moo.h
+++ b/moo/lib/moo.h
@@ -470,6 +470,10 @@ struct moo_dic_t
 typedef struct moo_nsdic_t moo_nsdic_t;
 typedef struct moo_nsdic_t* moo_oop_nsdic_t;
 
+#define MOO_METHOWNER_NAMED_INSTVARS 5
+typedef struct moo_methowner_t moo_methowner_t;
+typedef struct moo_methowner_t* moo_oop_methowner_t;
+
 #define MOO_INTERFACE_NAMED_INSTVARS 5
 typedef struct moo_interface_t moo_interface_t;
 typedef struct moo_interface_t* moo_oop_interface_t;
@@ -489,29 +493,62 @@ struct moo_nsdic_t
 	moo_oop_t nsup; /* a class if it belongs to the class. another nsdic if it doesn't */
 };
 
-struct moo_interface_t
+struct moo_methowner_t 
 {
+	/* a method can be owned by a class or an interface.
+	 * this structure defines common fields between a class and an interface and
+	 * is for internal VM use only. */
 	MOO_OBJ_HEADER;
+
+	/* === the following five fields must be placed in class and interface === */
 	moo_oop_char_t name;
 
 	/* [0] - instance methods, MethodDictionary
 	 * [1] - class methods, MethodDictionary */
 	moo_oop_dic_t  mthdic[2];      
+
 	moo_oop_nsdic_t nsup; /* pointer to the upper namespace */
 	moo_oop_nsdic_t nsdic; /* dictionary used for namespacing - may be nil when there are no subitems underneath */
+	/* ======================================================================== */
+};
+
+struct moo_interface_t
+{
+	MOO_OBJ_HEADER;
+
+	/* === the following five fields must be in sync with moo_methowner_t === */
+	moo_oop_char_t name;
+
+	/* [0] - instance methods, MethodDictionary
+	 * [1] - class methods, MethodDictionary */
+	moo_oop_dic_t  mthdic[2];      
+
+	moo_oop_nsdic_t nsup; /* pointer to the upper namespace */
+	moo_oop_nsdic_t nsdic; /* dictionary used for namespacing - may be nil when there are no subitems underneath */
+	/* ===================================================================== */
 };
 
 struct moo_class_t
 {
 	MOO_OBJ_HEADER;
 
+	/* === the following five fields must be in sync with moo_methowner_t === */
+	moo_oop_char_t name; /* Symbol */
+
+	/* [0] - instance methods, MethodDictionary
+	 * [1] - class methods, MethodDictionary */
+	moo_oop_dic_t  mthdic[2];      
+
+	moo_oop_nsdic_t nsup; /* pointer to the upper namespace */
+	moo_oop_nsdic_t nsdic; /* dictionary used for namespacing - may be nil when there are no subitems underneath */
+	/* ===================================================================== */
+
 	moo_oop_t      spec;          /* SmallInteger. instance specification */
 	moo_oop_t      selfspec;      /* SmallInteger. specification of the class object itself */
 
 	moo_oop_t      superclass;    /* Another class */
 	moo_oop_t      subclasses;    /* Array of subclasses */
 
-	moo_oop_char_t name;          /* Symbol */
 	moo_oop_t      modname;       /* Symbol if importing a module. nil if not. */
 
 	/* == NEVER CHANGE THIS ORDER OF 3 ITEMS BELOW == */
@@ -522,13 +559,6 @@ struct moo_class_t
 
 	moo_oop_char_t pooldics;      /* String - pool dictionaries imported */
 
-	/* [0] - instance methods, MethodDictionary
-	 * [1] - class methods, MethodDictionary */
-	moo_oop_dic_t  mthdic[2];      
-
-	moo_oop_nsdic_t nsup; /* pointer to the upper namespace */
-	moo_oop_nsdic_t nsdic; /* dictionary used for namespacing - may be nil when there are no subitems underneath */
-
 	moo_oop_t      trsize; /* trailer size for new instances */
 	moo_oop_t      trgc; /* trailer gc callback */
 
@@ -571,7 +601,7 @@ struct moo_method_t
 {
 	MOO_OBJ_HEADER;
 
-	moo_oop_class_t owner; /* Class */
+	moo_oop_methowner_t owner;  /* Class or Interface */
 
 	moo_oop_char_t  name; /* Symbol, method name */