diff --git a/contrib/tsearch2/rank.c b/contrib/tsearch2/rank.c
index 7bd5e1adf0..f5de5c7746 100644
--- a/contrib/tsearch2/rank.c
+++ b/contrib/tsearch2/rank.c
@@ -728,12 +728,28 @@ calc_rank_cd(float4 *arrdata, tsvector * txt, QUERYTYPE * query, int method)
 Datum
 rank_cd(PG_FUNCTION_ARGS)
 {
-	ArrayType  *win = (ArrayType *) PG_DETOAST_DATUM(PG_GETARG_DATUM(0));
+	ArrayType  *win;
 	tsvector   *txt = (tsvector *) PG_DETOAST_DATUM(PG_GETARG_DATUM(1));
 	QUERYTYPE  *query = (QUERYTYPE *) PG_DETOAST_DATUM_COPY(PG_GETARG_DATUM(2));
 	int			method = DEF_NORM_METHOD;
 	float4		res;
 
+	/*
+	 * Pre-8.2, rank_cd took just a plain int as its first argument.
+	 * It was a mistake to keep the same C function name while changing the
+	 * signature, but it's too late to fix that.  Instead, do a runtime test
+	 * to make sure the expected datatype has been passed.  This is needed
+	 * to prevent core dumps if tsearch2 function definitions from an old
+	 * database are loaded into an 8.2 server.
+	 */
+	if (get_fn_expr_argtype(fcinfo->flinfo, 0) != FLOAT4ARRAYOID)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
+				 errmsg("rank_cd() now takes real[] as its first argument, not integer")));
+
+	/* now safe to dereference the first arg */
+	win = (ArrayType *) PG_DETOAST_DATUM(PG_GETARG_DATUM(0));
+
 	if (ARR_NDIM(win) != 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
diff --git a/src/include/catalog/pg_type.h b/src/include/catalog/pg_type.h
index cb0c0e8574..b704637d43 100644
--- a/src/include/catalog/pg_type.h
+++ b/src/include/catalog/pg_type.h
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_type.h,v 1.173 2006/12/21 16:05:15 petere Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_type.h,v 1.174 2006/12/28 01:09:01 tgl Exp $
  *
  * NOTES
  *	  the genbki.sh script reads this file and generates .bki
@@ -422,6 +422,7 @@ DATA(insert OID = 1018 (  _lseg		 PGNSP PGUID -1 f b t \054 0 601 array_in array
 DATA(insert OID = 1019 (  _path		 PGNSP PGUID -1 f b t \054 0 602 array_in array_out array_recv array_send - d x f 0 -1 0 _null_ _null_ ));
 DATA(insert OID = 1020 (  _box		 PGNSP PGUID -1 f b t \073 0 603 array_in array_out array_recv array_send - d x f 0 -1 0 _null_ _null_ ));
 DATA(insert OID = 1021 (  _float4	 PGNSP PGUID -1 f b t \054 0 700 array_in array_out array_recv array_send - i x f 0 -1 0 _null_ _null_ ));
+#define FLOAT4ARRAYOID 1021
 DATA(insert OID = 1022 (  _float8	 PGNSP PGUID -1 f b t \054 0 701 array_in array_out array_recv array_send - d x f 0 -1 0 _null_ _null_ ));
 DATA(insert OID = 1023 (  _abstime	 PGNSP PGUID -1 f b t \054 0 702 array_in array_out array_recv array_send - i x f 0 -1 0 _null_ _null_ ));
 DATA(insert OID = 1024 (  _reltime	 PGNSP PGUID -1 f b t \054 0 703 array_in array_out array_recv array_send - i x f 0 -1 0 _null_ _null_ ));