diff --git a/src/backend/access/gin/ginscan.c b/src/backend/access/gin/ginscan.c
index 7ceea7a741b..77c0c577b50 100644
--- a/src/backend/access/gin/ginscan.c
+++ b/src/backend/access/gin/ginscan.c
@@ -295,6 +295,7 @@ ginNewScanKey(IndexScanDesc scan)
 		bool	   *partial_matches = NULL;
 		Pointer    *extra_data = NULL;
 		bool	   *nullFlags = NULL;
+		GinNullCategory *categories;
 		int32		searchMode = GIN_SEARCH_MODE_DEFAULT;
 
 		/*
@@ -346,15 +347,12 @@ ginNewScanKey(IndexScanDesc scan)
 		}
 
 		/*
-		 * If the extractQueryFn didn't create a nullFlags array, create one,
-		 * assuming that everything's non-null.  Otherwise, run through the
-		 * array and make sure each value is exactly 0 or 1; this ensures
-		 * binary compatibility with the GinNullCategory representation. While
-		 * at it, detect whether any null keys are present.
+		 * Create GinNullCategory representation.  If the extractQueryFn
+		 * didn't create a nullFlags array, we assume everything is non-null.
+		 * While at it, detect whether any null keys are present.
 		 */
-		if (nullFlags == NULL)
-			nullFlags = (bool *) palloc0(nQueryValues * sizeof(bool));
-		else
+		categories = (GinNullCategory *) palloc0(nQueryValues * sizeof(GinNullCategory));
+		if (nullFlags)
 		{
 			int32		j;
 
@@ -362,17 +360,16 @@ ginNewScanKey(IndexScanDesc scan)
 			{
 				if (nullFlags[j])
 				{
-					nullFlags[j] = true;	/* not any other nonzero value */
+					categories[j] = GIN_CAT_NULL_KEY;
 					hasNullQuery = true;
 				}
 			}
 		}
-		/* now we can use the nullFlags as category codes */
 
 		ginFillScanKey(so, skey->sk_attno,
 					   skey->sk_strategy, searchMode,
 					   skey->sk_argument, nQueryValues,
-					   queryValues, (GinNullCategory *) nullFlags,
+					   queryValues, categories,
 					   partial_matches, extra_data);
 	}
 
diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c
index d9c64834374..41d4b4fb6ff 100644
--- a/src/backend/access/gin/ginutil.c
+++ b/src/backend/access/gin/ginutil.c
@@ -529,19 +529,10 @@ ginExtractEntries(GinState *ginstate, OffsetNumber attnum,
 
 	/*
 	 * If the extractValueFn didn't create a nullFlags array, create one,
-	 * assuming that everything's non-null.  Otherwise, run through the array
-	 * and make sure each value is exactly 0 or 1; this ensures binary
-	 * compatibility with the GinNullCategory representation.
+	 * assuming that everything's non-null.
 	 */
 	if (nullFlags == NULL)
 		nullFlags = (bool *) palloc0(*nentries * sizeof(bool));
-	else
-	{
-		for (i = 0; i < *nentries; i++)
-			nullFlags[i] = (nullFlags[i] ? true : false);
-	}
-	/* now we can use the nullFlags as category codes */
-	*categories = (GinNullCategory *) nullFlags;
 
 	/*
 	 * If there's more than one key, sort and unique-ify.
@@ -600,6 +591,13 @@ ginExtractEntries(GinState *ginstate, OffsetNumber attnum,
 		pfree(keydata);
 	}
 
+	/*
+	 * Create GinNullCategory representation from nullFlags.
+	 */
+	*categories = (GinNullCategory *) palloc0(*nentries * sizeof(GinNullCategory));
+	for (i = 0; i < *nentries; i++)
+		(*categories)[i] = (nullFlags[i] ? GIN_CAT_NULL_KEY : GIN_CAT_NORM_KEY);
+
 	return entries;
 }
 
diff --git a/src/include/access/ginblock.h b/src/include/access/ginblock.h
index 114370c7d71..c3af3f03806 100644
--- a/src/include/access/ginblock.h
+++ b/src/include/access/ginblock.h
@@ -188,8 +188,11 @@ typedef struct
 
 /*
  * Category codes to distinguish placeholder nulls from ordinary NULL keys.
- * Note that the datatype size and the first two code values are chosen to be
- * compatible with the usual usage of bool isNull flags.
+ *
+ * The first two code values were chosen to be compatible with the usual usage
+ * of bool isNull flags.  However, casting between bool and GinNullCategory is
+ * risky because of the possibility of different bit patterns and type sizes,
+ * so it is no longer done.
  *
  * GIN_CAT_EMPTY_QUERY is never stored in the index; and notice that it is
  * chosen to sort before not after regular key values.