diff --git a/Source/DataSources/PolylineGeometryUpdater.js b/Source/DataSources/PolylineGeometryUpdater.js
index 87e1258e9005..530d49f94c6a 100644
--- a/Source/DataSources/PolylineGeometryUpdater.js
+++ b/Source/DataSources/PolylineGeometryUpdater.js
@@ -14,6 +14,7 @@ define([
         '../Core/GeometryInstance',
         '../Core/GroundPolylineGeometry',
         '../Core/Iso8601',
+        '../Core/oneTimeWarning',
         '../Core/PolylineGeometry',
         '../Core/PolylinePipeline',
         '../Core/ShowGeometryInstanceAttribute',
@@ -44,6 +45,7 @@ define([
         GeometryInstance,
         GroundPolylineGeometry,
         Iso8601,
+        oneTimeWarning,
         PolylineGeometry,
         PolylinePipeline,
         ShowGeometryInstanceAttribute,
@@ -521,6 +523,10 @@ define([
 
             this._clampToGround = defined(clampToGround) ? clampToGround.getValue(Iso8601.MINIMUM_VALUE) : false;
 
+            if (!this._clampToGround && defined(zIndex)) {
+                oneTimeWarning('Entity polylines must have clampToGround: true when using zIndex.  zIndex will be ignored.');
+            }
+
             this._dynamic = false;
             this._geometryChanged.raiseEvent(this);
         }