diff --git a/src/backend/utils/adt/varbit.c b/src/backend/utils/adt/varbit.c
index e947785..d1d0dd6 100644
--- a/src/backend/utils/adt/varbit.c
+++ b/src/backend/utils/adt/varbit.c
@@ -1187,7 +1187,7 @@ bit_overlay(VarBit *t1, VarBit *t2, int sp, int sl)
 Datum
 bitlength(PG_FUNCTION_ARGS)
 {
-	VarBit	   *arg = PG_GETARG_VARBIT_P(0);
+	VarBit	   *arg = PG_GETARG_VARBIT_P_SLICE(0,0,VARHDRSZ+VARBITHDRSZ);
 
 	PG_RETURN_INT32(VARBITLEN(arg));
 }
diff --git a/src/include/utils/varbit.h b/src/include/utils/varbit.h
index 2a4ec67..811efeb 100644
--- a/src/include/utils/varbit.h
+++ b/src/include/utils/varbit.h
@@ -36,9 +36,11 @@ typedef struct
  * BIT and BIT VARYING are toastable varlena types.  They are the same
  * as far as representation goes, so we just have one set of macros.
  */
+#define DatumGetVarBitPSlice(X,m,n)	((VarBit *) PG_DETOAST_DATUM_SLICE(X,m,n))
 #define DatumGetVarBitP(X)		   ((VarBit *) PG_DETOAST_DATUM(X))
 #define DatumGetVarBitPCopy(X)	   ((VarBit *) PG_DETOAST_DATUM_COPY(X))
 #define VarBitPGetDatum(X)		   PointerGetDatum(X)
+#define PG_GETARG_VARBIT_P_SLICE(n,a,b)	DatumGetVarBitPSlice(PG_GETARG_DATUM(n),a,b)
 #define PG_GETARG_VARBIT_P(n)	   DatumGetVarBitP(PG_GETARG_DATUM(n))
 #define PG_GETARG_VARBIT_P_COPY(n) DatumGetVarBitPCopy(PG_GETARG_DATUM(n))
 #define PG_RETURN_VARBIT_P(x)	   return VarBitPGetDatum(x)
diff --git a/src/test/regress/expected/bit.out b/src/test/regress/expected/bit.out
index 9c7d202..d440dbd 100644
--- a/src/test/regress/expected/bit.out
+++ b/src/test/regress/expected/bit.out
@@ -80,6 +80,20 @@ SELECT v, length(v) AS lv
  01010101010 | 11
 (4 rows)
 
+SELECT length(string_agg('1','')::BIT VARYING)
+	   FROM generate_series(1,1000) gs;
+ length 
+--------
+   1000
+(1 row)
+
+SELECT length(string_agg('1','')::BIT VARYING)
+	   FROM generate_series(1,65536) gs;
+ length 
+--------
+  65536
+(1 row)
+
 -- Substring
 SELECT b,
        SUBSTRING(b FROM 2 FOR 4) AS sub_2_4,
diff --git a/src/test/regress/sql/bit.sql b/src/test/regress/sql/bit.sql
index 419d47c..a60870c 100644
--- a/src/test/regress/sql/bit.sql
+++ b/src/test/regress/sql/bit.sql
@@ -40,6 +40,10 @@ SELECT b, length(b) AS lb
        FROM BIT_TABLE;
 SELECT v, length(v) AS lv
        FROM VARBIT_TABLE;
+SELECT length(string_agg('1','')::BIT VARYING)
+	   FROM generate_series(1,1000) gs;
+SELECT length(string_agg('1','')::BIT VARYING)
+	   FROM generate_series(1,65536) gs;
 
 -- Substring
 SELECT b,