2 files changed, 11 insertions, 1 deletions
diff --git a/src/mbgl/style/expression/compound_expression.cpp b/src/mbgl/style/expression/compound_expression.cpp
index f8c2376cb3..2e823ff43d 100644
--- a/src/mbgl/style/expression/compound_expression.cpp
+++ b/src/mbgl/style/expression/compound_expression.cpp
@@ -352,6 +352,15 @@ std::unordered_map<std::string, CompoundExpressionRegistry::Definition> initiali
         return *(params.colorRampParameter);
     });
 
+    define("line-progress", [](const EvaluationContext& params) -> Result<double> {
+        if (!params.colorRampParameter) {
+            return EvaluationError {
+                "The 'line-progress' expression is unavailable in the current evaluation context."
+            };
+        }
+        return *(params.colorRampParameter);
+    });
+
     define("has", [](const EvaluationContext& params, const std::string& key) -> Result<bool> {
         if (!params.feature) {
             return EvaluationError {
diff --git a/src/mbgl/style/expression/parsing_context.cpp b/src/mbgl/style/expression/parsing_context.cpp
index ef17caed33..3fe50aa1e4 100644
--- a/src/mbgl/style/expression/parsing_context.cpp
+++ b/src/mbgl/style/expression/parsing_context.cpp
@@ -69,7 +69,8 @@ bool isConstant(const Expression& expression) {
     }
     
     return isFeatureConstant(expression) &&
-        isGlobalPropertyConstant(expression, std::array<std::string, 2>{{"zoom", "heatmap-density"}});
+        isGlobalPropertyConstant(expression, std::array<std::string, 2>{{"zoom", "heatmap-density"}}) &&
+        isGlobalPropertyConstant(expression, std::array<std::string, 2>{{"zoom", "line-progress"}});
 }
 
 using namespace mbgl::style::conversion;