diff --git a/src/channeldef.ts b/src/channeldef.ts
index be2a615f74..d39fb4e798 100644
--- a/src/channeldef.ts
+++ b/src/channeldef.ts
@@ -86,7 +86,12 @@ import {isSignalRef} from './vega.schema';
 
 export type PrimitiveValue = number | string | boolean | null;
 
-export type Value = PrimitiveValue | number[] | Gradient | Text | ExprRef | SignalRef;
+export type Value<ES extends ExprRef | SignalRef = ExprRef | SignalRef> =
+  | PrimitiveValue
+  | number[]
+  | Gradient
+  | Text
+  | ES;
 
 /**
  * Definition object for a constant value (primitive value or gradient definition) of an encoding channel.
diff --git a/src/compile/mark/encode/valueref.ts b/src/compile/mark/encode/valueref.ts
index 9f68b88486..8fc951e149 100644
--- a/src/compile/mark/encode/valueref.ts
+++ b/src/compile/mark/encode/valueref.ts
@@ -28,6 +28,7 @@ import {
 } from '../../../channeldef';
 import {Config} from '../../../config';
 import {dateTimeToExpr, isDateTime} from '../../../datetime';
+import {isExprRef} from '../../../expr';
 import * as log from '../../../log';
 import {isPathMark, Mark, MarkDef} from '../../../mark';
 import {fieldValidPredicate} from '../../../predicate';
@@ -138,6 +139,8 @@ export function valueRefForFieldOrDatumDef(
       ref.signal = dateTimeToExpr(datum);
     } else if (isSignalRef(datum)) {
       ref.signal = datum.signal;
+    } else if (isExprRef(datum)) {
+      ref.signal = datum.expr;
     } else {
       ref.value = datum;
     }
diff --git a/src/vega.schema.ts b/src/vega.schema.ts
index 916955b4a7..82ff710d6d 100644
--- a/src/vega.schema.ts
+++ b/src/vega.schema.ts
@@ -92,7 +92,7 @@ export function isSignalRef(o: any): o is SignalRef {
 
 // TODO: add type of value (Make it VgValueRef<V extends ValueOrGradient> {value?:V ...})
 export interface VgValueRef {
-  value?: Value | number[];
+  value?: Value<null>;
   field?:
     | string
     | {
diff --git a/test/compile/mark/point.test.ts b/test/compile/mark/point.test.ts
index 9598f80286..32e9773b25 100644
--- a/test/compile/mark/point.test.ts
+++ b/test/compile/mark/point.test.ts
@@ -434,4 +434,17 @@ describe('Mark: Circle', () => {
 
     expect(filledCircleProps.stroke).toEqual({signal: "'red'"});
   });
+
+  it('converts expression in mark properties into signal', () => {
+    const filledCircleModel = parseUnitModelWithScaleAndLayoutSize({
+      mark: {type: 'circle'},
+      encoding: {
+        x: {datum: {expr: 'myX'}, type: 'quantitative'}
+      }
+    });
+
+    const filledCircleProps = circle.encodeEntry(filledCircleModel);
+
+    expect(filledCircleProps.x).toEqual({scale: 'x', signal: 'myX'});
+  });
 });