diff --git a/src/main/wacc/parser.scala b/src/main/wacc/parser.scala
index 7d76969..d8b52b4 100644
--- a/src/main/wacc/parser.scala
+++ b/src/main/wacc/parser.scala
@@ -175,7 +175,15 @@ object parser {
         `<rvalue>`.label("valid initial value for variable")
       )
       // TODO: Can we inline the name of the variable in the message
-      | Assign(`<lvalue>` <~ "=", `<rvalue>`)
+      | Assign(
+        `<lvalue>` <~ ("=" | "(".verifiedExplain(
+          "function calls must use the 'call' keyword and the result must be assigned to a variable"
+        )),
+        `<rvalue>`
+      ) |
+      ("call" ~> `<ident>`).verifiedExplain(
+        "function calls' results must be assigned to a variable"
+      )
   private lazy val `<lvalue>`: Parsley[LValue] =
     `<pair-elem>` | `<ident-or-array-elem>`
   private lazy val `<rvalue>`: Parsley[RValue] =