diff --git a/src/6model/reprs/VMArray.h b/src/6model/reprs/VMArray.h
index e30dd3596d..7b69121949 100644
--- a/src/6model/reprs/VMArray.h
+++ b/src/6model/reprs/VMArray.h
@@ -1,7 +1,7 @@
 /* Concurrent use of a VMArray is erroneous. This debugging option will
  * catch bad usages. (Eventually, we will refactor VMArray to not have
  * this issue.) */
-#define MVM_ARRAY_CONC_DEBUG 0
+#define MVM_ARRAY_CONC_DEBUG 1
 
 /* Representation used by VM-level arrays. Adopted from QRPA work by
  * Patrick Michaud. */
diff --git a/src/core/exceptions.c b/src/core/exceptions.c
index f5429fbc10..f199eba005 100644
--- a/src/core/exceptions.c
+++ b/src/core/exceptions.c
@@ -869,7 +869,7 @@ MVM_NO_RETURN void MVM_oops(MVMThreadContext *tc, const char *messageFormat, ...
     fprintf(stderr, "\n");
     MVM_dump_backtrace(tc);
     fprintf(stderr, "\n");
-    exit(1);
+    abort(); /// XXX Die horribly.
 }
 
 /* Throws an ad-hoc (untyped) exception. */
diff --git a/src/core/fixedsizealloc.c b/src/core/fixedsizealloc.c
index 4fe682f94c..f47d2adcd0 100644
--- a/src/core/fixedsizealloc.c
+++ b/src/core/fixedsizealloc.c
@@ -10,7 +10,7 @@
  * behavior. */
 
 /* Turn this on to switch to a mode where we debug by size. */
-#define FSA_SIZE_DEBUG 0
+#define FSA_SIZE_DEBUG 1
 #if FSA_SIZE_DEBUG
 typedef struct {
     MVMuint64 alloc_size;
diff --git a/src/gc/debug.h b/src/gc/debug.h
index d69423badc..839da90ed8 100644
--- a/src/gc/debug.h
+++ b/src/gc/debug.h
@@ -4,7 +4,7 @@
  * 2 = Checks on every object register access (slow)
  * 3 = Collects garbage on every allocation
  */
-#define MVM_GC_DEBUG 0
+#define MVM_GC_DEBUG 1
 
 #if MVM_GC_DEBUG
 #define MVM_ASSERT_NOT_FROMSPACE(tc, c) do { \
diff --git a/src/moar.h b/src/moar.h
index 1ee2434944..fe84ab8f9e 100644
--- a/src/moar.h
+++ b/src/moar.h
@@ -1,3 +1,4 @@
+#undef NDEBUG
 #include <stdlib.h>
 #include <stdarg.h>
 #include <stdio.h>
diff --git a/src/spesh/usages.h b/src/spesh/usages.h
index 499a55d1f8..af94d21ff9 100644
--- a/src/spesh/usages.h
+++ b/src/spesh/usages.h
@@ -1,5 +1,5 @@
 /* Option to enable checking of define/use chains for debugging purposes. */
-#define MVM_SPESH_CHECK_DU 0
+#define MVM_SPESH_CHECK_DU 1
 
 /* Usage information, which is held per SSA written register. */
 struct MVMSpeshUsages {
diff --git a/src/strings/uthash_types.h b/src/strings/uthash_types.h
index 8e89e97cbc..d8f6e69840 100644
--- a/src/strings/uthash_types.h
+++ b/src/strings/uthash_types.h
@@ -1,7 +1,7 @@
 #ifndef UTHASH_TYPES
 #define UTHASH_TYPES
 /* If set to 1, will throw if you add a key to the hash during iteration. */
-#define MVM_HASH_THROW_ON_ITER_AFTER_ADD_KEY 0
+#define MVM_HASH_THROW_ON_ITER_AFTER_ADD_KEY 1
 /* If set to 1, will randomize bucket iteration order and bucket insertion order.
  * HASH_ITER_FAST is not affected by iteration order randomization. */
 #define MVM_HASH_RANDOMIZE 1