3 files changed, 18 insertions, 4 deletions

diff --git a/migcom.c b/migcom.c
index c07e84d..e61c79b 100644
--- a/migcom.c
+++ b/migcom.c
@@ -213,7 +213,6 @@ main(int argc, char **argv)
     set_program_name("mig");
     parseArgs(argc, argv);
     init_global();
-    init_type();
 
     LookNormal();
     (void) yyparse();
diff --git a/parser.y b/parser.y
index 104f604..23294bf 100644
--- a/parser.y
+++ b/parser.y
@@ -212,6 +212,7 @@ Subsystem		:	SubsystemStart SubsystemMods
 	       IsKernelUser ? ", KernelUser" : "",
 	       IsKernelServer ? ", KernelServer" : "");
     }
+    init_type();
 }
 			;
 
@@ -238,7 +239,6 @@ SubsystemMod		:	syKernelUser
     IsKernelUser = TRUE;
     port_size = vm_offset_size;
     port_size_in_bits = vm_offset_size_in_bits;
-    init_type();
 }
 			|	syKernelServer
 {
@@ -247,7 +247,6 @@ SubsystemMod		:	syKernelUser
     IsKernelServer = TRUE;
     port_size = vm_offset_size;
     port_size_in_bits = vm_offset_size_in_bits;
-    init_type();
 }
 			;
 
@@ -351,7 +350,7 @@ TypeDecl		:	syType NamedTypeSpec
     identifier_t name = $2->itName;
 
     if (itLookUp(name) != itNULL)
-	warn("overriding previous definition of %s", name);
+		error("overriding previous definition of %s", name);
     itInsert(name, $2);
 }
 			;
diff --git a/type.c b/type.c
index 66944d9..3846746 100644
--- a/type.c
+++ b/type.c
@@ -57,6 +57,7 @@ ipc_type_t *itWaitTimeType;	/* used for dummy WaitTime args */
 ipc_type_t *itMsgOptionType;	/* used for dummy MsgOption args */
 ipc_type_t *itShortType;        /* used for the short type */
 ipc_type_t *itIntType;          /* used for the int type */
+static boolean_t types_initialized = FALSE;
 
 static ipc_type_t *list = itNULL;
 
@@ -67,6 +68,13 @@ static ipc_type_t *list = itNULL;
 ipc_type_t *
 itLookUp(identifier_t name)
 {
+    if (!types_initialized)
+    {
+        error("Basic types not initialized when looking up type %s. Did you "
+              "forget to define the subsystem?", name);
+        return NULL;
+    }
+
     ipc_type_t *it, **last;
 
     for (it = *(last = &list); it != itNULL; it = *(last = &it->itNext))
@@ -875,6 +883,14 @@ itMakeDeallocType(void)
 void
 init_type(void)
 {
+    if (types_initialized)
+    {
+        error("Basic types were already initialized");
+        exit(EXIT_FAILURE);
+    }
+    /* Mark initialization here since itInsert below will require it. */
+    types_initialized = TRUE;
+
     itByteType = itAlloc();
     itByteType->itName = "unsigned char";
     itByteType->itInName = MACH_MSG_TYPE_BYTE;