diff --git a/dataconv/share.go b/dataconv/share.go
index c8726131..2070b54d 100644
--- a/dataconv/share.go
+++ b/dataconv/share.go
@@ -272,6 +272,6 @@ func shardDictPerform(thread *starlark.Thread, b *starlark.Builtin, args starlar
 	case starlark.Callable:
 		return pr.CallInternal(thread, starlark.Tuple{d}, nil)
 	default:
-		return nil, fmt.Errorf("unsupported callable type: %s", pr.Type())
+		return nil, fmt.Errorf("%s: not callable type: %s", b.Name(), pr.Type())
 	}
 }
diff --git a/dataconv/share_test.go b/dataconv/share_test.go
index e807e5cf..3bf528a0 100644
--- a/dataconv/share_test.go
+++ b/dataconv/share_test.go
@@ -204,6 +204,14 @@ func TestSharedDict_Functions(t *testing.T) {
 				assert.eq(sd.len(), 1)
 			`),
 		},
+		{
+			name: `attr: custom len -- invalid args`,
+			script: itn.HereDoc(`
+				load('share', 'sd')
+				sd.len(123)
+			`),
+			wantErr: `len: got 1 arguments, want 0`,
+		},
 		{
 			name: `attr: custom perform`,
 			script: itn.HereDoc(`
@@ -215,6 +223,22 @@ func TestSharedDict_Functions(t *testing.T) {
 				print(sd)
 			`),
 		},
+		{
+			name: `attr: custom perform -- invalid args`,
+			script: itn.HereDoc(`
+				load('share', 'sd')
+				sd.perform()
+			`),
+			wantErr: `perform: missing argument for fn`,
+		},
+		{
+			name: `attr: custom perform -- invalid type`,
+			script: itn.HereDoc(`
+				load('share', 'sd')
+				sd.perform(123)
+			`),
+			wantErr: `perform: not callable type: int`,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {