diff --git a/src/engine/execute.js b/src/engine/execute.js
index 69468688e..e01908f58 100644
--- a/src/engine/execute.js
+++ b/src/engine/execute.js
@@ -201,21 +201,43 @@ const execute = function (sequencer, thread, recursiveCall) {
         blockCached._fieldKind = fieldKeys.length > 0 ? FieldKind.DYNAMIC : FieldKind.NONE;
         if (fieldKeys.length === 1 && fieldKeys.includes('VARIABLE')) {
             blockCached._fieldKind = FieldKind.VARIABLE;
-            blockCached._fieldVariable = {
-                id: fields.VARIABLE.id,
-                name: fields.VARIABLE.value
+            blockCached._argValues = {
+                VARIABLE: {
+                    id: fields.VARIABLE.id,
+                    name: fields.VARIABLE.value
+                },
+                mutation: blockCached.mutation
             };
         } else if (fieldKeys.length === 1 && fieldKeys.includes('LIST')) {
             blockCached._fieldKind = FieldKind.LIST;
-            blockCached._fieldList = {
-                id: fields.LIST.id,
-                name: fields.LIST.value
+            blockCached._argValues = {
+                LIST: {
+                    id: fields.LIST.id,
+                    name: fields.LIST.value
+                },
+                mutation: blockCached.mutation
             };
         } else if (fieldKeys.length === 1 && fieldKeys.includes('BROADCAST_OPTION')) {
             blockCached._fieldKind = FieldKind.BROADCAST_OPTION;
-            blockCached._fieldBroadcastOption = {
-                id: fields.BROADCAST_OPTION.id,
-                name: fields.BROADCAST_OPTION.value
+            blockCached._argValues = {
+                BROADCAST_OPTION: {
+                    id: fields.BROADCAST_OPTION.id,
+                    name: fields.BROADCAST_OPTION.value
+                },
+                mutation: blockCached.mutation
+            };
+        } else if (fieldKeys.length > 0) {
+            // FieldKind.DYNAMIC
+            blockCached._argValues = {
+                mutation: blockCached.mutation
+            };
+            for (const fieldName in fields) {
+                blockCached._argValues[fieldName] = fields[fieldName].value;
+            }
+        } else {
+            // FieldKind.NONE
+            blockCached._argValues = {
+                mutation: blockCached.mutation
             };
         }
 
@@ -228,9 +250,7 @@ const execute = function (sequencer, thread, recursiveCall) {
     }
 
     const opcode = blockCached.opcode;
-    const fields = blockCached._fields;
     const inputs = blockCached._inputs;
-    const mutation = blockCached.mutation;
     const blockFunction = blockCached._blockFunction;
     const isHat = blockCached._isHat;
 
@@ -260,29 +280,10 @@ const execute = function (sequencer, thread, recursiveCall) {
         return;
     }
 
-    // Generate values for arguments (inputs).
-    const argValues = {};
+    // Update values for arguments (inputs).
+    let argValues = blockCached._argValues;
 
-    // Add all fields on this block to the argValues. Some known fields may
-    // appear by themselves and can be set to argValues quicker by setting them
-    // explicitly.
-    if (blockCached._fieldKind !== FieldKind.NONE) {
-        switch (blockCached._fieldKind) {
-        case FieldKind.VARIABLE:
-            argValues.VARIABLE = blockCached._fieldVariable;
-            break;
-        case FieldKind.LIST:
-            argValues.LIST = blockCached._fieldList;
-            break;
-        case FieldKind.BROADCAST_OPTION:
-            argValues.BROADCAST_OPTION = blockCached._fieldBroadcastOption;
-            break;
-        default:
-            for (const fieldName in fields) {
-                argValues[fieldName] = fields[fieldName].value;
-            }
-        }
-    }
+    // Fields are set during blockCached initialization.
 
     // Recursively evaluate input blocks.
     for (const inputName in inputs) {
@@ -363,9 +364,6 @@ const execute = function (sequencer, thread, recursiveCall) {
         }
     }
 
-    // Add any mutation to args (e.g., for procedures).
-    argValues.mutation = mutation;
-
     let primitiveReportedValue = null;
     blockUtility.sequencer = sequencer;
     blockUtility.thread = thread;