diff --git a/ocaml/step3_env.ml b/ocaml/step3_env.ml
index 73d4236dd9..ef7d131675 100644
--- a/ocaml/step3_env.ml
+++ b/ocaml/step3_env.ml
@@ -33,6 +33,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match ast with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/step4_if_fn_do.ml b/ocaml/step4_if_fn_do.ml
index f08aa55223..0e0cbaf76f 100644
--- a/ocaml/step4_if_fn_do.ml
+++ b/ocaml/step4_if_fn_do.ml
@@ -21,6 +21,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match ast with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/step6_file.ml b/ocaml/step6_file.ml
index e9d48d3ffe..41b3a052c9 100644
--- a/ocaml/step6_file.ml
+++ b/ocaml/step6_file.ml
@@ -21,6 +21,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match ast with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/step7_quote.ml b/ocaml/step7_quote.ml
index 3291f48fba..23eaa740fc 100644
--- a/ocaml/step7_quote.ml
+++ b/ocaml/step7_quote.ml
@@ -33,6 +33,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match ast with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/step8_macros.ml b/ocaml/step8_macros.ml
index 7f61c597ca..93113e5ad5 100644
--- a/ocaml/step8_macros.ml
+++ b/ocaml/step8_macros.ml
@@ -54,6 +54,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match macroexpand ast env with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/step9_try.ml b/ocaml/step9_try.ml
index 2eab66eabb..1885359ffe 100644
--- a/ocaml/step9_try.ml
+++ b/ocaml/step9_try.ml
@@ -54,6 +54,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match macroexpand ast env with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value
diff --git a/ocaml/stepA_mal.ml b/ocaml/stepA_mal.ml
index fc43eb69a2..c36e6c87e3 100644
--- a/ocaml/stepA_mal.ml
+++ b/ocaml/stepA_mal.ml
@@ -54,6 +54,7 @@ let rec eval_ast ast env =
     | _ -> ast
 and eval ast env =
   match macroexpand ast env with
+    | T.List { T.value = [] } -> ast
     | T.List { T.value = [(T.Symbol { T.value = "def!" }); key; expr] } ->
         let value = (eval expr env) in
           Env.set env key value; value