diff --git a/engine/hashmap.c b/engine/hashmap.c
index 8504d7b..3e1ee05 100644
--- a/engine/hashmap.c
+++ b/engine/hashmap.c
@@ -261,6 +261,8 @@ static sxi32 HashmapGrowBucket(ph7_hashmap *pMap) {
  */
 static sxi32 HashmapInsertIntKey(ph7_hashmap *pMap, sxi64 iKey, ph7_value *pValue, sxu32 nRefIdx) {
 	ph7_hashmap_node *pNode;
+	sxu32 nValue = pValue ? pValue->nIdx : SXU32_HIGH;
+	sxi32 bArena = pValue && SySetAt(&pMap->pVm->aMemObj, nValue) == pValue;
 	sxu32 nIdx;
 	sxu32 nHash;
 	sxi32 rc;
@@ -271,11 +273,15 @@ static sxi32 HashmapInsertIntKey(ph7_hashmap *pMap, sxi64 iKey, ph7_value *pValu
 	if(pObj == 0) {
 		return SXERR_MEM;
 	}
+	nIdx = pObj->nIdx;
 	if(pValue) {
+		/* Reserve may move the source slot as well as the new destination. */
+		if(bArena) {
+			pValue = (ph7_value *)SySetAt(&pMap->pVm->aMemObj, nValue);
+		}
 		/* Duplicate the value */
 		PH7_MemObjStore(pValue, pObj);
 	}
-	nIdx = pObj->nIdx;
 	/* Hash the key */
 	nHash = pMap->xIntHash(iKey);
 	/* Allocate a new int node */
@@ -302,6 +308,8 @@ static sxi32 HashmapInsertIntKey(ph7_hashmap *pMap, sxi64 iKey, ph7_value *pValu
  */
 static sxi32 HashmapInsertBlobKey(ph7_hashmap *pMap, const void *pKey, sxu32 nKeyLen, ph7_value *pValue, sxu32 nRefIdx) {
 	ph7_hashmap_node *pNode;
+	sxu32 nValue = pValue ? pValue->nIdx : SXU32_HIGH;
+	sxi32 bArena = pValue && SySetAt(&pMap->pVm->aMemObj, nValue) == pValue;
 	sxu32 nHash;
 	sxu32 nIdx;
 	sxi32 rc;
@@ -312,11 +320,15 @@ static sxi32 HashmapInsertBlobKey(ph7_hashmap *pMap, const void *pKey, sxu32 nKe
 	if(pObj == 0) {
 		return SXERR_MEM;
 	}
+	nIdx = pObj->nIdx;
 	if(pValue) {
+		/* Reserve may move the source slot as well as the new destination. */
+		if(bArena) {
+			pValue = (ph7_value *)SySetAt(&pMap->pVm->aMemObj, nValue);
+		}
 		/* Duplicate the value */
 		PH7_MemObjStore(pValue, pObj);
 	}
-	nIdx = pObj->nIdx;
 	/* Hash the key */
 	nHash = pMap->xBlobHash(pKey, nKeyLen);
 	/* Allocate a new blob node */
diff --git a/engine/memobj.c b/engine/memobj.c
index fd44dd8..543ea47 100644
--- a/engine/memobj.c
+++ b/engine/memobj.c
@@ -399,13 +399,22 @@ PH7_PRIVATE sxi32 PH7_CheckVarCompat(ph7_value *pObj, int nType) {
  * destination are of the compatible data types.
  */
 PH7_PRIVATE sxi32 PH7_MemObjSafeStore(ph7_value *pSrc, ph7_value *pDest) {
+	/* Scalar destinations need not have initialized arena metadata. */
+	ph7_vm *pVm = (pSrc->nType & MEMOBJ_HASHMAP) ? pDest->pVm : 0;
+	sxu32 nDest = pVm ? pDest->nIdx : SXU32_HIGH;
+	sxi32 bArena = pVm && SySetAt(&pVm->aMemObj, nDest) == pDest;
 	if(pDest->nType == 0 || pDest->nType == MEMOBJ_NULL || pDest->nType == pSrc->nType) {
+		sxu32 nType = pSrc->nType;
 		PH7_MemObjStore(pSrc, pDest);
+		/* Array copies can move both source and destination arena slots. */
+		if(bArena) {
+			pDest = (ph7_value *)SySetAt(&pVm->aMemObj, nDest);
+		}
 		if(pDest->nType == 0 || pDest->nType == MEMOBJ_NULL) {
-			if(pSrc->nType == MEMOBJ_NULL) {
+			if(nType == MEMOBJ_NULL) {
 				pDest->nType = MEMOBJ_VOID;
 			} else {
-				pDest->nType = pSrc->nType;
+				pDest->nType = nType;
 			}
 		}
 	} else if(pDest->nType & MEMOBJ_MIXED) {
@@ -413,6 +422,9 @@ PH7_PRIVATE sxi32 PH7_MemObjSafeStore(ph7_value *pSrc, ph7_value *pDest) {
 			/* mixed[] */
 			if(pSrc->nType & MEMOBJ_HASHMAP) {
 				PH7_MemObjStore(pSrc, pDest);
+				if(bArena) {
+					pDest = (ph7_value *)SySetAt(&pVm->aMemObj, nDest);
+				}
 				pDest->nType |= MEMOBJ_MIXED;
 			} else if(pSrc->nType & MEMOBJ_NULL) {
 				PH7_MemObjToHashmap(pSrc);
@@ -946,12 +958,6 @@ PH7_PRIVATE sxi32 PH7_MemObjStore(ph7_value *pSrc, ph7_value *pDest) {
 		pObj = (ph7_class_instance *)pDest->x.pOther;
 	}
 	SyMemcpy((const void *) & (*pSrc), &(*pDest), sizeof(ph7_value) - (sizeof(ph7_vm *) + sizeof(SyBlob) + sizeof(sxu32)));
-	if(pSrcMap) {
-		ph7_hashmap *pMap;
-		pMap = PH7_NewHashmap(&(*pDest->pVm), 0, 0);
-		PH7_HashmapDup(pSrcMap, pMap);
-		pDest->x.pOther = pMap;
-	}
 	rc = SXRET_OK;
 	if(SyBlobLength(&pSrc->sBlob) > 0) {
 		SyBlobReset(&pDest->sBlob);
@@ -961,6 +967,20 @@ PH7_PRIVATE sxi32 PH7_MemObjStore(ph7_value *pSrc, ph7_value *pDest) {
 			SyBlobRelease(&pDest->sBlob);
 		}
 	}
+	if(pSrcMap) {
+		ph7_vm *pVm = pDest->pVm;
+		sxu32 nDest = pDest->nIdx;
+		sxi32 bArena = SySetAt(&pVm->aMemObj, nDest) == pDest;
+		ph7_hashmap *pMap;
+		/* Finish reading the source before recursive copies relocate aMemObj.
+		 * Stack destinations have no arena slot and must not be rebound. */
+		pMap = PH7_NewHashmap(pVm, 0, 0);
+		PH7_HashmapDup(pSrcMap, pMap);
+		if(bArena) {
+			pDest = (ph7_value *)SySetAt(&pVm->aMemObj, nDest);
+		}
+		pDest->x.pOther = pMap;
+	}
 	if(pObj) {
 		PH7_ClassInstanceUnref(pObj);
 	}