diff --git a/src/env.h b/src/env.h
index 01158bf0e..96e94ac39 100644
--- a/src/env.h
+++ b/src/env.h
@@ -178,7 +178,7 @@ class env_var_t {
     static env_var_flags_t flags_for(const wchar_t *name);
     static std::shared_ptr<const wcstring_list_t> empty_list();
 
-    env_var_t &operator=(const env_var_t &var) = default;
+    env_var_t &operator=(const env_var_t &) = default;
     env_var_t &operator=(env_var_t &&) = default;
 
     bool operator==(const env_var_t &rhs) const {
diff --git a/src/io.h b/src/io.h
index 4b1b09d7e..6ce2605a6 100644
--- a/src/io.h
+++ b/src/io.h
@@ -56,7 +56,7 @@ class separated_buffer_t {
 
     /// We may be moved.
     /// Note this leaves the moved-from value in a bogus state until clear() is called on it.
-    separated_buffer_t(separated_buffer_t &&rhs) = default;
+    separated_buffer_t(separated_buffer_t &&) = default;
     separated_buffer_t &operator=(separated_buffer_t &&) = default;
 
     /// Construct a separated_buffer_t with the given buffer limit \p limit, or 0 for no limit.
diff --git a/src/maybe.h b/src/maybe.h
index 6654718ec..8924a6b2b 100644
--- a/src/maybe.h
+++ b/src/maybe.h
@@ -179,8 +179,8 @@ class maybe_t : private maybe_detail::conditionally_copyable_t<T> {
 
     // Note that defaulting these allows these to be conditionally deleted via
     // conditionally_copyable_t().
-    maybe_t &operator=(const maybe_t &v) = default;
-    maybe_t &operator=(maybe_t &&v) = default;
+    maybe_t &operator=(const maybe_t &) = default;
+    maybe_t &operator=(maybe_t &&) = default;
 
     // Dereference support.
     const T *operator->() const { return &value(); }