diff --git a/doc/src/sgml/custom-scan.sgml b/doc/src/sgml/custom-scan.sgml
index 239ba29de7..0fd8494e45 100644
--- a/doc/src/sgml/custom-scan.sgml
+++ b/doc/src/sgml/custom-scan.sgml
@@ -73,8 +73,9 @@ typedef struct CustomPath
     the row-count estimate, start and total cost, and sort ordering provided
     by this path.  <structfield>flags</structfield> is a bit mask, which should include
     <literal>CUSTOMPATH_SUPPORT_BACKWARD_SCAN</literal> if the custom path can support
-    a backward scan and <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> if it
-    can support mark and restore.  Both capabilities are optional.
+    a backward scan, <literal>CUSTOMPATH_SUPPORT_MARK_RESTORE</literal> if it
+    can support mark and restore, and <literal>CUSTOMPATH_SUPPORT_PROJECTION</literal>
+    if it can support projections.  All capabilities are optional.
     An optional <structfield>custom_paths</structfield> is a list of <structname>Path</structname>
     nodes used by this custom-path node; these will be transformed into
     <structname>Plan</structname> nodes by planner.
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index a9aff24831..c9c8b140e5 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -7051,6 +7051,8 @@ is_projection_capable_path(Path *path)
 			 * get relaxed later.
 			 */
 			return false;
+		case T_CustomScan:
+			return castNode(CustomPath, path)->flags & CUSTOMPATH_SUPPORT_PROJECTION;
 		default:
 			break;
 	}
@@ -7089,6 +7091,8 @@ is_projection_capable_plan(Plan *plan)
 			 * get relaxed later.
 			 */
 			return false;
+		case T_CustomScan:
+			return castNode(CustomScan, plan)->flags & CUSTOMPATH_SUPPORT_PROJECTION;
 		default:
 			break;
 	}
diff --git a/src/include/nodes/extensible.h b/src/include/nodes/extensible.h
index 9e425e5651..7d3dc7e828 100644
--- a/src/include/nodes/extensible.h
+++ b/src/include/nodes/extensible.h
@@ -80,6 +80,7 @@ extern const ExtensibleNodeMethods *GetExtensibleNodeMethods(const char *name,
  */
 #define CUSTOMPATH_SUPPORT_BACKWARD_SCAN	0x0001
 #define CUSTOMPATH_SUPPORT_MARK_RESTORE		0x0002
+#define CUSTOMPATH_SUPPORT_PROJECTION			0x0004
 
 /*
  * Custom path methods.  Mostly, we just need to know how to convert a