diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 268a55e71f..360b26e6fc 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -464,6 +464,14 @@ brinrescan(PG_FUNCTION_ARGS)
 
 	/* other arguments ignored */
 
+	/*
+	 * Other index AMs preprocess the scan keys at this point, or sometime
+	 * early during the scan; this lets them optimize by removing redundant
+	 * keys, or doing early returns when they are impossible to satisfy; see
+	 * _bt_preprocess_keys for an example.  Something like that could be added
+	 * here someday, too.
+	 */
+
 	if (scankey && scan->numberOfKeys > 0)
 		memmove(scan->keyData, scankey,
 				scan->numberOfKeys * sizeof(ScanKeyData));
diff --git a/src/backend/access/brin/brin_inclusion.c b/src/backend/access/brin/brin_inclusion.c
index 803b07f10a..926487ec03 100644
--- a/src/backend/access/brin/brin_inclusion.c
+++ b/src/backend/access/brin/brin_inclusion.c
@@ -276,8 +276,14 @@ brin_inclusion_consistent(PG_FUNCTION_ARGS)
 		 * For IS NOT NULL, we can only skip ranges that are known to have
 		 * only nulls.
 		 */
-		Assert(key->sk_flags & SK_SEARCHNOTNULL);
-		PG_RETURN_BOOL(!column->bv_allnulls);
+		if (key->sk_flags & SK_SEARCHNOTNULL)
+			PG_RETURN_BOOL(!column->bv_allnulls);
+
+		/*
+		 * Neither IS NULL nor IS NOT NULL was used; assume all indexable
+		 * operators are strict and return false.
+		 */
+		PG_RETURN_BOOL(false);
 	}
 
 	/* If it is all nulls, it cannot possibly be consistent. */
diff --git a/src/backend/access/brin/brin_minmax.c b/src/backend/access/brin/brin_minmax.c
index 7cd98887c0..2cc6e41e5f 100644
--- a/src/backend/access/brin/brin_minmax.c
+++ b/src/backend/access/brin/brin_minmax.c
@@ -174,8 +174,14 @@ brin_minmax_consistent(PG_FUNCTION_ARGS)
 		 * For IS NOT NULL, we can only skip ranges that are known to have
 		 * only nulls.
 		 */
-		Assert(key->sk_flags & SK_SEARCHNOTNULL);
-		PG_RETURN_BOOL(!column->bv_allnulls);
+		if (key->sk_flags & SK_SEARCHNOTNULL)
+			PG_RETURN_BOOL(!column->bv_allnulls);
+
+		/*
+		 * Neither IS NULL nor IS NOT NULL was used; assume all indexable
+		 * operators are strict and return false.
+		 */
+		PG_RETURN_BOOL(false);
 	}
 
 	/* if the range is all empty, it cannot possibly be consistent */