diff --git a/include/groundvm.h b/include/groundvm.h
index 7fbad50..c10158f 100644
--- a/include/groundvm.h
+++ b/include/groundvm.h
@@ -31,6 +31,7 @@ typedef enum ListAccessStatus {
 
 struct GroundValue;
 struct GroundFunction;
+struct GroundStruct;
 
 struct List;
 
@@ -59,7 +60,7 @@ typedef struct GroundError {
 typedef struct GroundValue {
     GroundValueType type;
     struct GroundStruct* customType;
-    union {
+    struct {
         int64_t intVal;
         double doubleVal;
         char* stringVal;
diff --git a/src/types.h b/src/types.h
index 600322c..a288cc8 100644
--- a/src/types.h
+++ b/src/types.h
@@ -63,7 +63,7 @@ typedef struct GroundError {
 typedef struct GroundValue {
     GroundValueType type;
     struct GroundStruct* customType;
-    union {
+    struct {
         int64_t intVal;
         double doubleVal;
         char* stringVal;