diff --git a/src/interpreter.c b/src/interpreter.c
index 4288afe..38321bd 100644
--- a/src/interpreter.c
+++ b/src/interpreter.c
@@ -1332,9 +1332,9 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                     }
     
                     if (right->type == INT) {
-                        result += right->data.intVal;
+                        result -= right->data.intVal;
                     } else if (right->type == DOUBLE) {
-                        result += right->data.doubleVal;
+                        result -= right->data.doubleVal;
                     }
 
                     addVariable(scope->variables, in->args.args[2].value.refName, createDoubleGroundValue(result));
diff --git a/tests/log.txt b/tests/log.txt
new file mode 100644
index 0000000..e8a281a
--- /dev/null
+++ b/tests/log.txt
@@ -0,0 +1,6 @@
+Lists are deprecated, please migrate to using the "collections" library soon.
+Ground runtime error:
+  ErrorType: Hello
+  ErrorContext: [1, 2, 3, Hi!]
+  ErrorInstruction: error "Hello" [1, 2, 3, Hi!] 1
+  ErrorLine: 2