diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index a575afacab3..57a49be06b8 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -1454,7 +1454,7 @@ GinBufferStoreTuple(GinBuffer *buffer, GinTuple *tup)
 	if (GinBufferIsEmpty(buffer))
 	{
 		buffer->category = tup->category;
-		buffer->keylen = tup->keylen;
+		buffer->keylen = tup->u.keylen;
 		buffer->attnum = tup->attrnum;
 
 		buffer->typlen = tup->typlen;
@@ -2238,7 +2238,7 @@ _gin_build_tuple(OffsetNumber attrnum, unsigned char category,
 	char	   *ptr;
 
 	Size		tuplen;
-	int			keylen;
+	Size		keylen;
 
 	dlist_mutable_iter iter;
 	dlist_head	segments;
@@ -2314,7 +2314,7 @@ _gin_build_tuple(OffsetNumber attrnum, unsigned char category,
 	tuple->tuplen = tuplen;
 	tuple->attrnum = attrnum;
 	tuple->category = category;
-	tuple->keylen = keylen;
+	tuple->u.keylen = keylen;
 	tuple->nitems = nitems;
 
 	/* key type info */
@@ -2387,7 +2387,7 @@ _gin_parse_tuple_key(GinTuple *a)
 
 	if (a->typbyval)
 	{
-		memcpy(&key, a->data, a->keylen);
+		memcpy(&key, a->data, a->u.keylen);
 		return key;
 	}
 
@@ -2406,8 +2406,8 @@ _gin_parse_tuple_items(GinTuple *a)
 	int			ndecoded;
 	ItemPointer items;
 
-	len = a->tuplen - SHORTALIGN(offsetof(GinTuple, data) + a->keylen);
-	ptr = (char *) a + SHORTALIGN(offsetof(GinTuple, data) + a->keylen);
+	len = a->tuplen - SHORTALIGN(offsetof(GinTuple, data) + a->u.keylen);
+	ptr = (char *) a + SHORTALIGN(offsetof(GinTuple, data) + a->u.keylen);
 
 	items = ginPostingListDecodeAllSegments((GinPostingList *) ptr, len, &ndecoded);
 
diff --git a/src/include/access/gin_tuple.h b/src/include/access/gin_tuple.h
index 702f7d12889..3c3345ca0ef 100644
--- a/src/include/access/gin_tuple.h
+++ b/src/include/access/gin_tuple.h
@@ -21,7 +21,25 @@ typedef struct GinTuple
 {
 	int			tuplen;			/* length of the whole tuple */
 	OffsetNumber attrnum;		/* attnum of index key */
-	uint16		keylen;			/* bytes in data for key value */
+
+	/*
+	 * The key value is accessed in place, so data (below) must be aligned
+	 * well enough for any key type.  We include both "double" and "int64" in
+	 * the union to ensure that the compiler knows it must be MAXALIGN'ed (cf.
+	 * configure's computation of MAXIMUM_ALIGNOF); this puts data at a
+	 * MAXALIGN'ed offset, which the static assertion below verifies.  On
+	 * 64-bit platforms, this already happens anyway; this trick is only
+	 * needed on some 32-bit platforms.  Note that putting a flexible array
+	 * member into a union is not valid C, so we have to pick some other
+	 * member to move the alignment around.  This one just happens to be a
+	 * space-efficient one.
+	 */
+	union
+	{
+		Size		keylen;		/* bytes in data for key value */
+		double		force_align_d;
+		int64		force_align_i64;
+	}			u;
 	int16		typlen;			/* typlen for key */
 	bool		typbyval;		/* typbyval for key */
 	signed char category;		/* category: normal or NULL? */
@@ -29,12 +47,15 @@ typedef struct GinTuple
 	char		data[FLEXIBLE_ARRAY_MEMBER];
 } GinTuple;
 
+StaticAssertDecl(offsetof(GinTuple, data) % MAXIMUM_ALIGNOF == 0,
+				 "GinTuple.data must be MAXALIGN'ed");
+
 static inline ItemPointer
 GinTupleGetFirst(GinTuple *tup)
 {
 	GinPostingList *list;
 
-	list = (GinPostingList *) SHORTALIGN(tup->data + tup->keylen);
+	list = (GinPostingList *) SHORTALIGN(tup->data + tup->u.keylen);
 
 	return &list->first;
 }