diff --git a/src/esqlite3.erl b/src/esqlite3.erl
index 22c8fa3..93f03cc 100644
--- a/src/esqlite3.erl
+++ b/src/esqlite3.erl
@@ -243,9 +243,11 @@ bind(Stmt, Args, Timeout) ->
 
 %% @doc Return the column names of the prepared statement.
 %%
+-spec column_names(statement()) -> tuple(atom()).
 column_names(Stmt) ->
     column_names(Stmt, ?DEFAULT_TIMEOUT).
 
+-spec column_names(statement(), timeout()) -> tuple(atom()).
 column_names(Stmt, Timeout) ->
     Ref = make_ref(),
     ok = esqlite3_nif:column_names(Stmt, Ref, self()),