diff --git a/src/sfall_arrays.cc b/src/sfall_arrays.cc
index c561151..3b805e9 100644
--- a/src/sfall_arrays.cc
+++ b/src/sfall_arrays.cc
@@ -104,7 +104,17 @@ ProgramValue GetArrayKey(ArrayId array_id, int index)
     if (index == -1) { // special index to indicate if array is associative
         throw(std::invalid_argument("Not implemented yet"));
     };
+    // TODO: if assoc
     return SFallArrayElement(index);
 }
 
+int LenArray(ArrayId array_id)
+{
+    auto arr = get_array_by_id(array_id);
+    if (arr == nullptr) {
+        return -1;
+    };
+    return arr->size();
+}
+
 }
\ No newline at end of file
diff --git a/src/sfall_opcodes.cc b/src/sfall_opcodes.cc
index 6c92042..c9db981 100644
--- a/src/sfall_opcodes.cc
+++ b/src/sfall_opcodes.cc
@@ -335,8 +335,7 @@ static void opGetArray(Program* program)
 static void opLenArray(Program* program)
 {
     auto arrayId = programStackPopInteger(program);
-
-    programStackPushInteger(program, 100);
+    programStackPushInteger(program, LenArray(arrayId));
 }
 
 // party_member_list