diff --git a/examples/gno.land/r/gnoland/faucet/z2_filetest.gno b/examples/gno.land/r/gnoland/faucet/z2_filetest.gno
index 1791cd91989..9b59d7c07d3 100644
--- a/examples/gno.land/r/gnoland/faucet/z2_filetest.gno
+++ b/examples/gno.land/r/gnoland/faucet/z2_filetest.gno
@@ -16,11 +16,11 @@ func main() {
 	)
 	std.TestSetOrigCaller(adminaddr)
 	err := faucet.AdminAddController(controlleraddr1)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	err = faucet.AdminAddController(controlleraddr2)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	println(faucet.Render(""))
diff --git a/examples/gno.land/r/gnoland/faucet/z3_filetest.gno b/examples/gno.land/r/gnoland/faucet/z3_filetest.gno
index 1dca56811a9..682a619256a 100644
--- a/examples/gno.land/r/gnoland/faucet/z3_filetest.gno
+++ b/examples/gno.land/r/gnoland/faucet/z3_filetest.gno
@@ -18,21 +18,21 @@ func main() {
 	)
 	std.TestSetOrigCaller(adminaddr)
 	err := faucet.AdminAddController(controlleraddr1)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	err = faucet.AdminAddController(controlleraddr2)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	std.TestSetOrigCaller(controlleraddr1)
 	err = faucet.Transfer(testaddr1, 1000000)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	std.TestSetOrigCaller(controlleraddr2)
 	err = faucet.Transfer(testaddr1, 2000000)
-	if err != nil {
+	if err != "" {
 		panic(err)
 	}
 	println(faucet.Render(""))
diff --git a/gnovm/pkg/gnolang/preprocess.go b/gnovm/pkg/gnolang/preprocess.go
index a4576fa6f48..6b77f5562a0 100644
--- a/gnovm/pkg/gnolang/preprocess.go
+++ b/gnovm/pkg/gnolang/preprocess.go
@@ -1012,6 +1012,29 @@ func Preprocess(store Store, ctx BlockNode, n Node) Node {
 								args1 = Preprocess(nil, last, args1).(Expr)
 								n.Args[1] = args1
 							}
+						} else {
+							var tx *constTypeExpr // array type expr, lazily initialized
+							// Another special case for append: adding untyped constants.
+							// They must be converted to the array type for consistency.
+							for i, arg := range n.Args[1:] {
+								if _, ok := arg.(*ConstExpr); !ok {
+									// Consider only constant expressions.
+									continue
+								}
+								if t1 := evalStaticTypeOf(store, last, arg); t1 != nil && !isUntyped(t1) {
+									// Consider only untyped values (including nil).
+									continue
+								}
+
+								if tx == nil {
+									// Get the array type from the first argument.
+									s0 := evalStaticTypeOf(store, last, n.Args[0])
+									tx = constType(arg, s0.Elem())
+								}
+								// Convert to the array type.
+								arg1 := Call(tx, arg)
+								n.Args[i+1] = Preprocess(nil, last, arg1).(Expr)
+							}
 						}
 					} else if fv.PkgPath == uversePkgPath && fv.Name == "copy" {
 						if len(n.Args) == 2 {
diff --git a/gnovm/pkg/gnolang/values_conversions.go b/gnovm/pkg/gnolang/values_conversions.go
index e2000defdde..66d8bcbf233 100644
--- a/gnovm/pkg/gnolang/values_conversions.go
+++ b/gnovm/pkg/gnolang/values_conversions.go
@@ -77,6 +77,10 @@ GNO_CASE:
 	}
 	// special case for undefined/nil source
 	if tv.IsUndefined() {
+		switch t.Kind() {
+		case BoolKind, StringKind, IntKind, Int8Kind, Int16Kind, Int32Kind, Int64Kind, UintKind, Uint8Kind, Uint16Kind, Uint32Kind, Uint64Kind, Float32Kind, Float64Kind, BigintKind, BigdecKind:
+			panic(fmt.Sprintf("cannot convert %v to %v", tv, t))
+		}
 		tv.T = t
 		return
 	}
diff --git a/gnovm/tests/files/append5.gno b/gnovm/tests/files/append5.gno
index b1fdae852b1..0eba5a46463 100644
--- a/gnovm/tests/files/append5.gno
+++ b/gnovm/tests/files/append5.gno
@@ -7,4 +7,4 @@ func main() {
 }
 
 // Output:
-// X
+// X
\ No newline at end of file
diff --git a/gnovm/tests/files/append6.gno b/gnovm/tests/files/append6.gno
new file mode 100644
index 00000000000..523c57bf044
--- /dev/null
+++ b/gnovm/tests/files/append6.gno
@@ -0,0 +1,12 @@
+package main
+
+func main() {
+	const x = 118999
+	y := 11
+	p := []int{}
+	p = append(p, x, y)
+	println(p[0] + p[1])
+}
+
+// Output:
+// 119010
diff --git a/gnovm/tests/files/append7.gno b/gnovm/tests/files/append7.gno
new file mode 100644
index 00000000000..85783724205
--- /dev/null
+++ b/gnovm/tests/files/append7.gno
@@ -0,0 +1,10 @@
+package main
+
+func main() {
+	var errors []error
+	errors = append(errors, nil, nil)
+	println(len(errors))
+}
+
+// Output:
+// 2
diff --git a/gnovm/tests/files/convert4.gno b/gnovm/tests/files/convert4.gno
new file mode 100644
index 00000000000..6ad748499ed
--- /dev/null
+++ b/gnovm/tests/files/convert4.gno
@@ -0,0 +1,7 @@
+package main
+
+func main() {
+	println(int(nil))
+}
+
+// error: cannot convert (undefined) to int
diff --git a/gnovm/tests/files/convert5.gno b/gnovm/tests/files/convert5.gno
new file mode 100644
index 00000000000..acd33889ff0
--- /dev/null
+++ b/gnovm/tests/files/convert5.gno
@@ -0,0 +1,9 @@
+package main
+
+func main() {
+	var ints []int
+	ints = append(ints, nil, nil)
+	println(ints)
+}
+
+// error: cannot convert (undefined) to int