diff --git a/assert.go b/assert.go
index 6351355..b87d514 100644
--- a/assert.go
+++ b/assert.go
@@ -1 +1,13 @@
+//go:build !XX_DISABLE_ASSERT
+
 package xx
+
+func Assert(cond bool) {
+	if !cond {
+		panic("assertion failed")
+	}
+}
+
+func Unreachable() {
+	panic("unreachable")
+}
diff --git a/assert_disabled.go b/assert_disabled.go
index 6351355..eaf4237 100644
--- a/assert_disabled.go
+++ b/assert_disabled.go
@@ -1 +1,7 @@
+//go:build XX_DISABLE_ASSERT
+
 package xx
+
+func Assert(cond bool) {}
+
+func Unreachable() {}
diff --git a/spmd/spmd.go b/spmd/spmd.go
index 17192ec..ba74e41 100644
--- a/spmd/spmd.go
+++ b/spmd/spmd.go
@@ -114,12 +114,14 @@ func (l Lane) Sync() {
 }
 
 // Store sends 'value' to all lanes.
+//
 // Store can be called concurrently.
 func (l Lane) Store(key, value any) {
 	l.state.userdata.Store(key, value)
 }
 
 // Load fetches a named value, returning nil if it does not exist.
+//
 // Load can be called concurrently.
 func (l Lane) Load(key any) any {
 	v, ok := l.state.userdata.Load(key)