diff --git a/src/machine.cpp b/src/machine.cpp
index 4b6d12d8ae..36c7780bb8 100644
--- a/src/machine.cpp
+++ b/src/machine.cpp
@@ -1571,6 +1571,11 @@ makeArrayClass(Thread* t, object spec)
 void
 removeMonitor(Thread* t, object o)
 {
+  unsigned hash;
+  if (DebugMonitors) {
+    hash = objectHash(t, o);
+  }
+
   object p = hashMapRemove(t, t->m->monitorMap, o, objectHash, objectEqual);
 
   assert(t, p);
@@ -1578,7 +1583,7 @@ removeMonitor(Thread* t, object o)
   if (DebugMonitors) {
     fprintf(stderr, "dispose monitor %p for object %x\n",
             static_cast<System::Monitor*>(pointerValue(t, p)),
-            objectHash(t, o));
+            hash);
   }
 
   static_cast<System::Monitor*>(pointerValue(t, p))->dispose();
diff --git a/src/machine.h b/src/machine.h
index dcf771f148..4ea31165e7 100644
--- a/src/machine.h
+++ b/src/machine.h
@@ -2015,11 +2015,16 @@ objectMonitor(Thread* t, object o, bool createNew);
 inline void
 acquire(Thread* t, object o)
 {
+  unsigned hash;
+  if (DebugMonitors) {
+    hash = objectHash(t, o);
+  }
+
   System::Monitor* m = objectMonitor(t, o, true);
 
   if (DebugMonitors) {
     fprintf(stderr, "thread %p acquires %p for %x\n",
-            t, m, objectHash(t, o));
+            t, m, hash);
   }
 
   acquire(t, m);
@@ -2028,11 +2033,16 @@ acquire(Thread* t, object o)
 inline void
 release(Thread* t, object o)
 {
+  unsigned hash;
+  if (DebugMonitors) {
+    hash = objectHash(t, o);
+  }
+
   System::Monitor* m = objectMonitor(t, o, false);
 
   if (DebugMonitors) {
     fprintf(stderr, "thread %p releases %p for %x\n",
-            t, m, objectHash(t, o));
+            t, m, hash);
   }
 
   release(t, m);
@@ -2041,11 +2051,16 @@ release(Thread* t, object o)
 inline void
 wait(Thread* t, object o, int64_t milliseconds)
 {
+  unsigned hash;
+  if (DebugMonitors) {
+    hash = objectHash(t, o);
+  }
+
   System::Monitor* m = objectMonitor(t, o, false);
 
   if (DebugMonitors) {
     fprintf(stderr, "thread %p waits %"LLD" millis on %p for %x\n",
-            t, milliseconds, m, objectHash(t, o));
+            t, milliseconds, m, hash);
   }
 
   if (m and m->owner() == t->systemThread) {
@@ -2063,7 +2078,7 @@ wait(Thread* t, object o, int64_t milliseconds)
 
   if (DebugMonitors) {
     fprintf(stderr, "thread %p wakes up on %p for %x\n",
-            t, m, objectHash(t, o));
+            t, m, hash);
   }
 
   stress(t);
@@ -2072,11 +2087,16 @@ wait(Thread* t, object o, int64_t milliseconds)
 inline void
 notify(Thread* t, object o)
 {
+  unsigned hash;
+  if (DebugMonitors) {
+    hash = objectHash(t, o);
+  }
+
   System::Monitor* m = objectMonitor(t, o, false);
 
   if (DebugMonitors) {
     fprintf(stderr, "thread %p notifies on %p for %x\n",
-            t, m, objectHash(t, o));
+            t, m, hash);
   }
 
   if (m and m->owner() == t->systemThread) {
diff --git a/src/util.cpp b/src/util.cpp
index c7579ee839..76cd74069c 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -102,24 +102,31 @@ void
 hashMapInsert(Thread* t, object map, object key, object value,
                uint32_t (*hash)(Thread*, object))
 {
+  // note that we reinitialize the array and index variables whenever
+  // an allocation (and thus possibly a collection) occurs, in case
+  // the array changes due to a table resize.
+
+  PROTECT(t, map);
+
+  uint32_t h = hash(t, key);
+
   bool weak = objectClass(t, map)
     == arrayBody(t, t->m->types, Machine::WeakHashMapType);
 
   object array = hashMapArray(t, map);
-  PROTECT(t, array);
 
   ++ hashMapSize(t, map);
 
   if (array == 0 or hashMapSize(t, map) >= arrayLength(t, array) * 2) { 
-    PROTECT(t, map);
     PROTECT(t, key);
     PROTECT(t, value);
 
     hashMapResize(t, map, hash, array ? arrayLength(t, array) * 2 : 16);
+
     array = hashMapArray(t, map);
   }
 
-  unsigned index = hash(t, key) & (arrayLength(t, array) - 1);
+  object k = key;
 
   if (weak) {
     PROTECT(t, key);
@@ -128,10 +135,17 @@ hashMapInsert(Thread* t, object map, object key, object value,
     object r = makeWeakReference(t, 0, 0, 0, 0);
     jreferenceTarget(t, r) = key;
     jreferenceVmNext(t, r) = t->m->weakReferences;
-    key = t->m->weakReferences = r;
+    k = t->m->weakReferences = r;
+
+    array = hashMapArray(t, map);
   }
 
-  object n = makeTriple(t, key, value, arrayBody(t, array, index));
+  unsigned index = h & (arrayLength(t, array) - 1);
+
+  object n = makeTriple(t, k, value, arrayBody(t, array, index));
+
+  array = hashMapArray(t, map);
+  index = h & (arrayLength(t, array) - 1);
 
   set(t, array, ArrayBody + (index * BytesPerWord), n);
 }