diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index c86f83e1dac..707c3b77f12 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -1125,7 +1125,26 @@ AllocSetFree(void *pointer)
 		Assert(FreeListIdxIsValid(fidx));
 		link = GetFreeListLink(chunk);
 
+		/*
+		 * It might seem odd that we use elevel ERROR for double-pfree but
+		 * only WARNING for write-past-chunk-end.  But the two conditions are
+		 * not very comparable.  In the double-pfree case we can prevent
+		 * corruption before it happens; while if we let it go through, the
+		 * result would be a corrupted freelist that allows this chunk to get
+		 * re-allocated twice.  Thus the original bug could cascade into
+		 * hard-to-understand misbehavior that might manifest far away from
+		 * the actual source of the problem.  On the other hand, a write past
+		 * chunk end can be relatively benign if just a few bytes too many
+		 * were written: often, only padding or unused space gets affected.
+		 * Moreover, whatever damage was done is already done, and we're just
+		 * reporting after the fact with no ability to clean it up.  So just
+		 * warn, like AllocSetCheck would do if the chunk didn't get freed.
+		 */
 #ifdef MEMORY_CONTEXT_CHECKING
+		/* Test for previously-freed chunk */
+		if (unlikely(chunk->requested_size == InvalidAllocSize))
+			elog(ERROR, "detected double pfree in %s %p",
+				 set->header.name, chunk);
 		/* Test for someone scribbling on unused space in chunk */
 		if (chunk->requested_size < GetChunkSizeFromFreeListIdx(fidx))
 			if (!sentinel_ok(pointer, chunk->requested_size))
@@ -1316,6 +1335,11 @@ AllocSetRealloc(void *pointer, Size size, int flags)
 	oldchksize = GetChunkSizeFromFreeListIdx(fidx);
 
 #ifdef MEMORY_CONTEXT_CHECKING
+	/* See comments in AllocSetFree about uses of ERROR and WARNING here */
+	/* Test for previously-freed chunk */
+	if (unlikely(chunk->requested_size == InvalidAllocSize))
+		elog(ERROR, "detected realloc of freed chunk in %s %p",
+			 set->header.name, chunk);
 	/* Test for someone scribbling on unused space in chunk */
 	if (chunk->requested_size < oldchksize)
 		if (!sentinel_ok(pointer, chunk->requested_size))
diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index 0238c111d2f..f19890d0e53 100644
--- a/src/backend/utils/mmgr/generation.c
+++ b/src/backend/utils/mmgr/generation.c
@@ -733,6 +733,11 @@ GenerationFree(void *pointer)
 	}
 
 #ifdef MEMORY_CONTEXT_CHECKING
+	/* See comments in AllocSetFree about uses of ERROR and WARNING here */
+	/* Test for previously-freed chunk */
+	if (unlikely(chunk->requested_size == InvalidAllocSize))
+		elog(ERROR, "detected double pfree in %s %p",
+			 ((MemoryContext) block->context)->name, chunk);
 	/* Test for someone scribbling on unused space in chunk */
 	Assert(chunk->requested_size < chunksize);
 	if (!sentinel_ok(pointer, chunk->requested_size))
@@ -838,6 +843,11 @@ GenerationRealloc(void *pointer, Size size, int flags)
 	set = block->context;
 
 #ifdef MEMORY_CONTEXT_CHECKING
+	/* See comments in AllocSetFree about uses of ERROR and WARNING here */
+	/* Test for previously-freed chunk */
+	if (unlikely(chunk->requested_size == InvalidAllocSize))
+		elog(ERROR, "detected realloc of freed chunk in %s %p",
+			 ((MemoryContext) set)->name, chunk);
 	/* Test for someone scribbling on unused space in chunk */
 	Assert(chunk->requested_size < oldsize);
 	if (!sentinel_ok(pointer, chunk->requested_size))
diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index 3e15d59683f..0f0148746b8 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -514,6 +514,7 @@ SlabAllocSetupNewChunk(MemoryContext context, SlabBlock *block,
 	MemoryChunkSetHdrMask(chunk, block, MAXALIGN(slab->chunkSize), MCTX_SLAB_ID);
 
 #ifdef MEMORY_CONTEXT_CHECKING
+	chunk->requested_size = size;
 	/* slab mark to catch clobber of "unused" space */
 	Assert(slab->chunkSize < (slab->fullChunkSize - Slab_CHUNKHDRSZ));
 	set_sentinel(MemoryChunkGetPointer(chunk), size);
@@ -720,11 +721,18 @@ SlabFree(void *pointer)
 	slab = block->slab;
 
 #ifdef MEMORY_CONTEXT_CHECKING
+	/* See comments in AllocSetFree about uses of ERROR and WARNING here */
+	/* Test for previously-freed chunk */
+	if (unlikely(chunk->requested_size == InvalidAllocSize))
+		elog(ERROR, "detected double pfree in %s %p",
+			 slab->header.name, chunk);
 	/* Test for someone scribbling on unused space in chunk */
 	Assert(slab->chunkSize < (slab->fullChunkSize - Slab_CHUNKHDRSZ));
 	if (!sentinel_ok(pointer, slab->chunkSize))
 		elog(WARNING, "detected write past chunk end in %s %p",
 			 slab->header.name, chunk);
+	/* Reset requested_size to InvalidAllocSize in free chunks */
+	chunk->requested_size = InvalidAllocSize;
 #endif
 
 	/* push this chunk onto the head of the block's free list */