diff --git a/_demo/ctxcancel/ctx.go b/_demo/ctxcancel/ctx.go
new file mode 100644
index 00000000..3b9afc26
--- /dev/null
+++ b/_demo/ctxcancel/ctx.go
@@ -0,0 +1,39 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+func main() {
+	// gen generates integers in a separate goroutine and
+	// sends them to the returned channel.
+	// The callers of gen need to cancel the context once
+	// they are done consuming generated integers not to leak
+	// the internal goroutine started by gen.
+	gen := func(ctx context.Context) <-chan int {
+		dst := make(chan int)
+		n := 1
+		go func() {
+			for {
+				select {
+				case <-ctx.Done():
+					return // returning not to leak the goroutine
+				case dst <- n:
+					n++
+				}
+			}
+		}()
+		return dst
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel() // cancel when we are finished consuming integers
+
+	for n := range gen(ctx) {
+		fmt.Println(n)
+		if n == 5 {
+			break
+		}
+	}
+}
diff --git a/ssa/expr.go b/ssa/expr.go
index 0010b014..2aed82c3 100644
--- a/ssa/expr.go
+++ b/ssa/expr.go
@@ -127,7 +127,7 @@ func (p Program) Zero(t Type) Expr {
 		default:
 			panic("todo")
 		}
-	case *types.Pointer:
+	case *types.Pointer, *types.Signature, *types.Chan:
 		return Expr{llvm.ConstNull(t.ll), t}
 	case *types.Struct:
 		n := u.NumFields()