diff --git a/interpreter.h b/interpreter.h
index 8fe6d7c..bca3458 100644
--- a/interpreter.h
+++ b/interpreter.h
@@ -515,6 +515,7 @@ void TypeParseIdentPart(struct ParseState *Parser, struct ValueType *BasicTyp, s
 void TypeParse(struct ParseState *Parser, struct ValueType **Typ, char **Identifier, int *IsStatic);
 struct ValueType *TypeGetMatching(Picoc *pc, struct ParseState *Parser, struct ValueType *ParentType, enum BaseType Base, int ArraySize, const char *Identifier, int AllowDuplicates);
 struct ValueType *TypeCreateOpaqueStruct(Picoc *pc, struct ParseState *Parser, const char *StructName, int Size);
+int TypeIsForwardDeclared(struct ParseState *Parser, struct ValueType *Typ);
 
 /* heap.c */
 void HeapInit(Picoc *pc, int StackSize);
diff --git a/tests/56_cross_structure.c b/tests/56_cross_structure.c
new file mode 100644
index 0000000..f8f333d
--- /dev/null
+++ b/tests/56_cross_structure.c
@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+struct s1;
+
+struct s2
+{
+    struct s1 *s;
+};
+
+struct s1
+{
+    struct s2 *s;
+};
+
+void main()
+{
+    printf("ok\n");
+}
diff --git a/tests/56_cross_structure.expect b/tests/56_cross_structure.expect
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/tests/56_cross_structure.expect
@@ -0,0 +1 @@
+ok
diff --git a/tests/Makefile b/tests/Makefile
index a73199a..a160023 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -49,7 +49,8 @@ TESTS=	00_assignment.test \
 	51_static.test \
 	52_unnamed_enum.test \
 	54_goto.test \
-	55_array_initialiser.test
+	55_array_initialiser.test \
+	56_cross_structure.test
 
 %.test: %.expect %.c
 	@echo Test: $*...
diff --git a/type.c b/type.c
index f7c8cb8..18fad9a 100644
--- a/type.c
+++ b/type.c
@@ -198,15 +198,18 @@ void TypeParseStruct(struct ParseState *Parser, struct ValueType **Typ, int IsSt
         StructIdentifier = PlatformMakeTempName(pc, TempNameBuf);
     }
 
-    *Typ = TypeGetMatching(pc, Parser, &Parser->pc->UberType, IsStruct ? TypeStruct : TypeUnion, 0, StructIdentifier, Token != TokenLeftBrace);
+    *Typ = TypeGetMatching(pc, Parser, &Parser->pc->UberType, IsStruct ? TypeStruct : TypeUnion, 0, StructIdentifier, TRUE);
+    if (Token == TokenLeftBrace && (*Typ)->Members != NULL)
+        ProgramFail(Parser, "data type '%t' is already defined", *Typ);
 
     Token = LexGetToken(Parser, NULL, FALSE);
     if (Token != TokenLeftBrace)
     { 
         /* use the already defined structure */
+#if 0
         if ((*Typ)->Members == NULL)
             ProgramFail(Parser, "structure '%s' isn't defined", LexValue->Val->Identifier);
-            
+#endif            
         return;
     }
     
@@ -527,3 +530,14 @@ void TypeParse(struct ParseState *Parser, struct ValueType **Typ, char **Identif
     TypeParseIdentPart(Parser, BasicType, Typ, Identifier);
 }
 
+/* check if a type has been fully defined - otherwise it's just a forward declaration */
+int TypeIsForwardDeclared(struct ParseState *Parser, struct ValueType *Typ)
+{
+    if (Typ->Base == TypeArray)
+        return TypeIsForwardDeclared(Parser, Typ->FromType);
+    
+    if ( (Typ->Base == TypeStruct || Typ->Base == TypeUnion) && Typ->Members == NULL)
+        return TRUE;
+        
+    return FALSE;
+}
diff --git a/variable.c b/variable.c
index 08659ed..d9de066 100644
--- a/variable.c
+++ b/variable.c
@@ -185,6 +185,10 @@ struct Value *VariableDefineButIgnoreIdentical(struct ParseState *Parser, char *
     int DeclLine;
     int DeclColumn;
     
+    /* is the type a forward declaration? */
+    if (TypeIsForwardDeclared(Parser, Typ))
+        ProgramFail(Parser, "type '%t' isn't defined", Typ);
+
     if (IsStatic)
     {
         char MangledName[LINEBUFFER_MAX];