diff --git a/mps/code/config.h b/mps/code/config.h
index 3e6158c1c7c..d68d1b52361 100644
--- a/mps/code/config.h
+++ b/mps/code/config.h
@@ -147,7 +147,9 @@
  *     cc -O2 -c -DCONFIG_PLINTH_NONE mps.c
  */
 
-#if defined(CONFIG_PLINTH_NONE)
+#if !defined(CONFIG_PLINTH_NONE)
+#define PLINTH
+#else
 #define PLINTH_NONE
 #endif
 
@@ -172,7 +174,9 @@
  */
 
 #if defined(CONFIG_THREAD_SINGLE)
-#define DISABLE_LOCKS
+#define LOCK
+#else
+#define LOCK_NONE
 #endif
 
 
@@ -190,8 +194,11 @@
 #if !defined(CONFIG_THREAD_SINGLE)
 #error "CONFIG_POLL_NONE without CONFIG_THREAD_SINGLE"
 #endif
-#define DISABLE_REMEMBERED_SET
-#define DISABLE_SHIELD
+#define REMEMBERED_SET
+#define SHIELD
+#else
+#define REMEMBERED_SET_NONE
+#define SHIELD_NONE
 #endif
 
 
diff --git a/mps/code/lock.h b/mps/code/lock.h
index 5f0cadd7065..4fcd591a0f2 100644
--- a/mps/code/lock.h
+++ b/mps/code/lock.h
@@ -195,8 +195,9 @@ extern void LockClaimGlobal(void);
 extern void LockReleaseGlobal(void);
 
 
-#ifdef DISABLE_LOCKS
-
+#if defined(LOCK)
+/* Nothing to do: functions declared in all lock configurations. */
+#elif defined(LOCK_NONE)
 #define LockSize() MPS_PF_ALIGN
 #define LockInit(lock) UNUSED(lock)
 #define LockFinish(lock) UNUSED(lock)
@@ -209,8 +210,9 @@ extern void LockReleaseGlobal(void);
 #define LockReleaseGlobalRecursive()
 #define LockClaimGlobal()
 #define LockReleaseGlobal()
-
-#endif  /* DISABLE_LOCKS */
+#else
+#error "No lock configuration."
+#endif  /* LOCK */
 
 
 #endif /* lock_h */
diff --git a/mps/code/mpm.h b/mps/code/mpm.h
index 7876330de65..8c030acaa77 100644
--- a/mps/code/mpm.h
+++ b/mps/code/mpm.h
@@ -524,14 +524,16 @@ extern void (ArenaEnter)(Arena arena);
 extern void (ArenaLeave)(Arena arena);
 extern void (ArenaPoll)(Globals globals);
 
-#ifdef DISABLE_SHIELD
+#if defined(SHIELD)
 #define ArenaEnter(arena)  UNUSED(arena)
 #define ArenaLeave(arena)  AVER(arena->busyTraces == TraceSetEMPTY)
 #define ArenaPoll(globals)  UNUSED(globals)
-#else
+#elif defined(SHIELD_NONE)
 #define ArenaEnter(arena)  ArenaEnterLock(arena, FALSE)
 #define ArenaLeave(arena)  ArenaLeaveLock(arena, FALSE)
-#endif
+#else
+#error "No shield configuration."
+#endif  /* SHIELD */
 
 extern void ArenaEnterRecursive(Arena arena);
 extern void ArenaLeaveRecursive(Arena arena);
@@ -892,7 +894,9 @@ extern void (ShieldSuspend)(Arena arena);
 extern void (ShieldResume)(Arena arena);
 extern void (ShieldFlush)(Arena arena);
 
-#ifdef DISABLE_SHIELD
+#if defined(SHIELD)
+/* Nothing to do: functions declared in all shield configurations. */
+#elif defined(SHIELD_NONE)
 #define ShieldRaise(arena, seg, mode) \
   BEGIN UNUSED(arena); UNUSED(seg); UNUSED(mode); END
 #define ShieldLower(arena, seg, mode) \
@@ -906,7 +910,9 @@ extern void (ShieldFlush)(Arena arena);
 #define ShieldSuspend(arena) BEGIN UNUSED(arena); END
 #define ShieldResume(arena) BEGIN UNUSED(arena); END
 #define ShieldFlush(arena) BEGIN UNUSED(arena); END
-#endif  /* DISABLE_SHIELD */
+#else
+#error "No shield configuration."
+#endif  /* SHIELD */
 
 
 /* Protection Interface
diff --git a/mps/code/mps.c b/mps/code/mps.c
index 2125d2d4a3c..200f63e894c 100644
--- a/mps/code/mps.c
+++ b/mps/code/mps.c
@@ -91,7 +91,7 @@
 
 /* ANSI Plinth */
 
-#if !defined(PLINTH_NONE)       /* see CONFIG_PLINTH_NONE in config.h  */
+#if defined(PLINTH)     /* see CONFIG_PLINTH_NONE in config.h  */
 #include "mpsliban.c"
 #include "mpsioan.c"
 #endif
diff --git a/mps/code/seg.c b/mps/code/seg.c
index dea2b7d7ff7..62a7397dfeb 100644
--- a/mps/code/seg.c
+++ b/mps/code/seg.c
@@ -309,12 +309,17 @@ void SegSetSummary(Seg seg, RefSet summary)
   AVERT(Seg, seg);
   AVER(summary == RefSetEMPTY || SegRankSet(seg) != RankSetEMPTY);
 
-#ifdef DISABLE_REMEMBERED_SET
+#if defined(REMEMBERED_SET)
+/* Nothing to do. */
+#elif defined(REMEMBERED_SET_NONE)
   /* Without protection, we can't maintain the remembered set because
      there are writes we don't know about. TODO: rethink this when
      implementating control. */
   summary = RefSetUNIV;
-#endif
+#else
+#error "No remembered set configuration."
+#endif  /* REMEMBERED_SET */
+
   if (summary != SegSummary(seg))
     seg->class->setSummary(seg, summary);
 }