diff --git a/doc/src/sgml/gist.sgml b/doc/src/sgml/gist.sgml
index b3cc347e5c..1648eb3672 100644
--- a/doc/src/sgml/gist.sgml
+++ b/doc/src/sgml/gist.sgml
@@ -267,14 +267,14 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
   </para>
 
  <para>
-   There are seven methods that an index operator class for
-   <acronym>GiST</acronym> must provide, and two that are optional.
+   There are five methods that an index operator class for
+   <acronym>GiST</acronym> must provide, and four that are optional.
    Correctness of the index is ensured
    by proper implementation of the <function>same</>, <function>consistent</>
    and <function>union</> methods, while efficiency (size and speed) of the
    index will depend on the <function>penalty</> and <function>picksplit</>
    methods.
-   The remaining two basic methods are <function>compress</> and
+   Two optional methods are <function>compress</> and
    <function>decompress</>, which allow an index to have internal tree data of
    a different type than the data it indexes. The leaves are to be of the
    indexed data type, while the other tree nodes can be of any C struct (but
@@ -285,7 +285,8 @@ CREATE INDEX ON my_table USING GIST (my_inet_column inet_ops);
    The optional eighth method is <function>distance</>, which is needed
    if the operator class wishes to support ordered scans (nearest-neighbor
    searches). The optional ninth method <function>fetch</> is needed if the
-   operator class wishes to support index-only scans.
+   operator class wishes to support index-only scans, except when the
+   <function>compress</> method is omitted.
  </para>
 
  <variablelist>
@@ -468,8 +469,10 @@ my_union(PG_FUNCTION_ARGS)
      <term><function>compress</></term>
      <listitem>
       <para>
-       Converts the data item into a format suitable for physical storage in
+       Converts a data item into a format suitable for physical storage in
        an index page.
+       If the <function>compress</> method is omitted, data items are stored
+       in the index without modification.
       </para>
 
       <para>
@@ -527,9 +530,17 @@ my_compress(PG_FUNCTION_ARGS)
      <term><function>decompress</></term>
      <listitem>
       <para>
-       The reverse of the <function>compress</function> method.  Converts the
-       index representation of the data item into a format that can be
-       manipulated by the other GiST methods in the operator class.
+       Converts the stored representation of a data item into a format that
+       can be manipulated by the other GiST methods in the operator class.
+       If the <function>decompress</> method is omitted, it is assumed that
+       the other GiST methods can work directly on the stored data format.
+       (<function>decompress</> is not necessarily the reverse of
+       the <function>compress</function> method; in particular,
+       if <function>compress</function> is lossy then it's impossible
+       for <function>decompress</> to exactly reconstruct the original
+       data.  <function>decompress</> is not necessarily equivalent
+       to <function>fetch</>, either, since the other GiST methods might not
+       require full reconstruction of the data.)
       </para>
 
       <para>
@@ -555,7 +566,8 @@ my_decompress(PG_FUNCTION_ARGS)
 </programlisting>
 
         The above skeleton is suitable for the case where no decompression
-        is needed.
+        is needed.  (But, of course, omitting the method altogether is even
+        easier, and is recommended in such cases.)
       </para>
      </listitem>
     </varlistentry>
@@ -883,7 +895,9 @@ LANGUAGE C STRICT;
         struct, whose <structfield>key</> field contains the same datum in its
         original, uncompressed form. If the opclass's compress function does
         nothing for leaf entries, the <function>fetch</> method can return the
-        argument as-is.
+        argument as-is.  Or, if the opclass does not have a compress function,
+        the <function>fetch</> method can be omitted as well, since it would
+        necessarily be a no-op.
        </para>
 
        <para>
diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 565525bbdf..aec174cd00 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -1453,12 +1453,23 @@ initGISTstate(Relation index)
 		fmgr_info_copy(&(giststate->unionFn[i]),
 					   index_getprocinfo(index, i + 1, GIST_UNION_PROC),
 					   scanCxt);
-		fmgr_info_copy(&(giststate->compressFn[i]),
-					   index_getprocinfo(index, i + 1, GIST_COMPRESS_PROC),
-					   scanCxt);
-		fmgr_info_copy(&(giststate->decompressFn[i]),
-					   index_getprocinfo(index, i + 1, GIST_DECOMPRESS_PROC),
-					   scanCxt);
+
+		/* opclasses are not required to provide a Compress method */
+		if (OidIsValid(index_getprocid(index, i + 1, GIST_COMPRESS_PROC)))
+			fmgr_info_copy(&(giststate->compressFn[i]),
+						   index_getprocinfo(index, i + 1, GIST_COMPRESS_PROC),
+						   scanCxt);
+		else
+			giststate->compressFn[i].fn_oid = InvalidOid;
+
+		/* opclasses are not required to provide a Decompress method */
+		if (OidIsValid(index_getprocid(index, i + 1, GIST_DECOMPRESS_PROC)))
+			fmgr_info_copy(&(giststate->decompressFn[i]),
+						   index_getprocinfo(index, i + 1, GIST_DECOMPRESS_PROC),
+						   scanCxt);
+		else
+			giststate->decompressFn[i].fn_oid = InvalidOid;
+
 		fmgr_info_copy(&(giststate->penaltyFn[i]),
 					   index_getprocinfo(index, i + 1, GIST_PENALTY_PROC),
 					   scanCxt);
@@ -1468,6 +1479,7 @@ initGISTstate(Relation index)
 		fmgr_info_copy(&(giststate->equalFn[i]),
 					   index_getprocinfo(index, i + 1, GIST_EQUAL_PROC),
 					   scanCxt);
+
 		/* opclasses are not required to provide a Distance method */
 		if (OidIsValid(index_getprocid(index, i + 1, GIST_DISTANCE_PROC)))
 			fmgr_info_copy(&(giststate->distanceFn[i]),
diff --git a/src/backend/access/gist/gistget.c b/src/backend/access/gist/gistget.c
index 760ea0c997..06dac0bb53 100644
--- a/src/backend/access/gist/gistget.c
+++ b/src/backend/access/gist/gistget.c
@@ -801,11 +801,13 @@ gistgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
  * Can we do index-only scans on the given index column?
  *
  * Opclasses that implement a fetch function support index-only scans.
+ * Opclasses without compression functions also support index-only scans.
  */
 bool
 gistcanreturn(Relation index, int attno)
 {
-	if (OidIsValid(index_getprocid(index, attno, GIST_FETCH_PROC)))
+	if (OidIsValid(index_getprocid(index, attno, GIST_FETCH_PROC)) ||
+		!OidIsValid(index_getprocid(index, attno, GIST_COMPRESS_PROC)))
 		return true;
 	else
 		return false;
diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index b6ccc1a66a..26d89f79ae 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -550,6 +550,11 @@ gistdentryinit(GISTSTATE *giststate, int nkey, GISTENTRY *e,
 		GISTENTRY  *dep;
 
 		gistentryinit(*e, k, r, pg, o, l);
+
+		/* there may not be a decompress function in opclass */
+		if (!OidIsValid(giststate->decompressFn[nkey].fn_oid))
+			return;
+
 		dep = (GISTENTRY *)
 			DatumGetPointer(FunctionCall1Coll(&giststate->decompressFn[nkey],
 											  giststate->supportCollation[nkey],
@@ -585,10 +590,14 @@ gistFormTuple(GISTSTATE *giststate, Relation r,
 
 			gistentryinit(centry, attdata[i], r, NULL, (OffsetNumber) 0,
 						  isleaf);
-			cep = (GISTENTRY *)
-				DatumGetPointer(FunctionCall1Coll(&giststate->compressFn[i],
-												  giststate->supportCollation[i],
-												  PointerGetDatum(&centry)));
+			/* there may not be a compress function in opclass */
+			if (OidIsValid(giststate->compressFn[i].fn_oid))
+				cep = (GISTENTRY *)
+					DatumGetPointer(FunctionCall1Coll(&giststate->compressFn[i],
+													  giststate->supportCollation[i],
+													  PointerGetDatum(&centry)));
+			else
+				cep = &centry;
 			compatt[i] = cep->key;
 		}
 	}
@@ -648,6 +657,17 @@ gistFetchTuple(GISTSTATE *giststate, Relation r, IndexTuple tuple)
 			else
 				fetchatt[i] = (Datum) 0;
 		}
+		else if (giststate->compressFn[i].fn_oid == InvalidOid)
+		{
+			/*
+			 * If opclass does not provide compress method that could change
+			 * original value, att is necessarily stored in original form.
+			 */
+			if (!isnull[i])
+				fetchatt[i] = datum;
+			else
+				fetchatt[i] = (Datum) 0;
+		}
 		else
 		{
 			/*
@@ -934,6 +954,20 @@ gistproperty(Oid index_oid, int attno,
 								 ObjectIdGetDatum(opcintype),
 								 ObjectIdGetDatum(opcintype),
 								 Int16GetDatum(procno));
+
+	/*
+	 * Special case: even without a fetch function, AMPROP_RETURNABLE is true
+	 * if the opclass has no compress function.
+	 */
+	if (prop == AMPROP_RETURNABLE && !*res)
+	{
+		*res = !SearchSysCacheExists4(AMPROCNUM,
+									  ObjectIdGetDatum(opfamily),
+									  ObjectIdGetDatum(opcintype),
+									  ObjectIdGetDatum(opcintype),
+									  Int16GetDatum(GIST_COMPRESS_PROC));
+	}
+
 	return true;
 }
 
diff --git a/src/backend/access/gist/gistvalidate.c b/src/backend/access/gist/gistvalidate.c
index 42254c5f15..42f91ac0c9 100644
--- a/src/backend/access/gist/gistvalidate.c
+++ b/src/backend/access/gist/gistvalidate.c
@@ -258,7 +258,8 @@ gistvalidate(Oid opclassoid)
 		if (opclassgroup &&
 			(opclassgroup->functionset & (((uint64) 1) << i)) != 0)
 			continue;			/* got it */
-		if (i == GIST_DISTANCE_PROC || i == GIST_FETCH_PROC)
+		if (i == GIST_DISTANCE_PROC || i == GIST_FETCH_PROC ||
+			i == GIST_COMPRESS_PROC || i == GIST_DECOMPRESS_PROC)
 			continue;			/* optional methods */
 		ereport(INFO,
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),