diff --git a/lib/strings/strings.ww b/lib/strings/strings.ww
index 1c306dba..b004ad30 100644
--- a/lib/strings/strings.ww
+++ b/lib/strings/strings.ww
@@ -99,12 +99,11 @@ export fn dup(s: str) str = {
 	r.ptr = nil;
 	r.len = 0;
 	if (s.len == 0) { return r; };
-	let buf: *u8 = rt.malloc(s.len: u64): *u8;
+	let buf: []u8 = alloc([], s.len: u64)!;
 	let i: i32 = 0;
 	for (i < s.len) { buf[i] = s[i]; i += 1; };
-	r.ptr = buf;
-	r.len = s.len;
-	return r;
+	buf.len = s.len;
+	return fromutf8_unsafe(buf);
 };
 
 // dupall — fresh `[]str` whose elements are independent copies of
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index e3ace8a2..c7f92ea3 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -1938,12 +1938,11 @@ export fn dup(s: str) str = {
 	r.ptr = nil;
 	r.len = 0;
 	if (s.len == 0) { return r; };
-	let buf: *u8 = rt.malloc(s.len: u64): *u8;
+	let buf: []u8 = alloc([], s.len: u64)!;
 	let i: i32 = 0;
 	for (i < s.len) { buf[i] = s[i]; i += 1; };
-	r.ptr = buf;
-	r.len = s.len;
-	return r;
+	buf.len = s.len;
+	return fromutf8_unsafe(buf);
 };
 
 // dupall — fresh `[]str` whose elements are independent copies of
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index d1334983..172596af 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -1938,12 +1938,11 @@ export fn dup(s: str) str = {
 	r.ptr = nil;
 	r.len = 0;
 	if (s.len == 0) { return r; };
-	let buf: *u8 = rt.malloc(s.len: u64): *u8;
+	let buf: []u8 = alloc([], s.len: u64)!;
 	let i: i32 = 0;
 	for (i < s.len) { buf[i] = s[i]; i += 1; };
-	r.ptr = buf;
-	r.len = s.len;
-	return r;
+	buf.len = s.len;
+	return fromutf8_unsafe(buf);
 };
 
 // dupall — fresh `[]str` whose elements are independent copies of
diff --git a/selfhost/test/smoke.combined.ww b/selfhost/test/smoke.combined.ww
index 3339fda9..e611545d 100644
--- a/selfhost/test/smoke.combined.ww
+++ b/selfhost/test/smoke.combined.ww
@@ -1828,12 +1828,11 @@ export fn dup(s: str) str = {
 	r.ptr = nil;
 	r.len = 0;
 	if (s.len == 0) { return r; };
-	let buf: *u8 = rt.malloc(s.len: u64): *u8;
+	let buf: []u8 = alloc([], s.len: u64)!;
 	let i: i32 = 0;
 	for (i < s.len) { buf[i] = s[i]; i += 1; };
-	r.ptr = buf;
-	r.len = s.len;
-	return r;
+	buf.len = s.len;
+	return fromutf8_unsafe(buf);
 };
 
 // dupall — fresh `[]str` whose elements are independent copies of