--- a/dom/animation/TimingParams.cpp
+++ b/dom/animation/TimingParams.cpp
@@ -133,16 +133,17 @@ TimingParams::ParseEasing(const nsAStrin
         case eCSSUnit_Enumerated:
           // Return Nothing() if "linear" is passed in.
           if (list->mValue.GetIntValue() ==
               NS_STYLE_TRANSITION_TIMING_FUNCTION_LINEAR) {
             return Nothing();
           }
           MOZ_FALLTHROUGH;
         case eCSSUnit_Cubic_Bezier:
+        case eCSSUnit_Function:
         case eCSSUnit_Steps: {
           nsTimingFunction timingFunction;
           nsRuleNode::ComputeTimingFunction(list->mValue, timingFunction);
           ComputedTimingFunction computedTimingFunction;
           computedTimingFunction.Init(timingFunction);
           return Some(computedTimingFunction);
         }
         default: