diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index 2d9f6d7aa0..17886c8411 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -533,7 +533,7 @@ pub fn (s string) index(p string) ?int {
 }
 
 // KMP search
-pub fn (s string) index_kmp(p string) int {
+fn (s string) index_kmp(p string) int {
         if p.len > s.len {
                 return -1
         }
@@ -572,9 +572,9 @@ pub fn (s string) index_any(chars string) int {
 	return -1
 }
 
-pub fn (s string) last_index(p string) int {
+pub fn (s string) last_index(p string) ?int {
 	if p.len > s.len {
-		return -1
+		return none
 	}
 	mut i := s.len - p.len
 	for i >= 0 {
@@ -587,7 +587,7 @@ pub fn (s string) last_index(p string) int {
 		}
 		i--
 	}
-	return -1
+	return none
 }
 
 pub fn (s string) index_after(p string, start int) int {
@@ -672,8 +672,10 @@ pub fn (s string) ends_with(p string) bool {
 	if p.len > s.len {
 		return false
 	}
-	res := s.last_index(p) == s.len - p.len
-	return res
+	idx := s.last_index(p) or {
+		return false
+	}
+	return idx == s.len - p.len
 }
 
 // TODO only works with ASCII
@@ -1069,16 +1071,14 @@ pub fn (s string) all_before(dot string) string {
 }
 
 pub fn (s string) all_before_last(dot string) string {
-	pos := s.last_index(dot)
-	if pos == -1 {
+	pos := s.last_index(dot) or {
 		return s
 	}
 	return s.left(pos)
 }
 
 pub fn (s string) all_after(dot string) string {
-	pos := s.last_index(dot)
-	if pos == -1 {
+	pos := s.last_index(dot) or {
 		return s
 	}
 	return s.right(pos + dot.len)
diff --git a/vlib/compiler/main.v b/vlib/compiler/main.v
index f7c297ef04..3c4be47b02 100644
--- a/vlib/compiler/main.v
+++ b/vlib/compiler/main.v
@@ -759,11 +759,13 @@ pub fn (v &V)  get_user_files() []string {
 	// v volt/slack_test.v: compile all .v files to get the environment
 	// I need to implement user packages! TODO
 	is_test_with_imports := dir.ends_with('_test.v') &&
-	(dir.contains('${os.path_separator}volt') || dir.contains('${os.path_separator}c2volt'))// TODO
+		(dir.contains('${os.path_separator}volt') ||
+		dir.contains('${os.path_separator}c2volt'))// TODO
 	if is_test_with_imports {
 		user_files << dir
-		pos := dir.last_index(os.path_separator)
-		dir = dir[..pos] + os.path_separator// TODO why is this needed
+		if pos := dir.last_index(os.path_separator) {
+			dir = dir[..pos] + os.path_separator// TODO why is this needed
+		}
 	}
 	if dir.ends_with('.v') || dir.ends_with('.vsh') {
 		// Just compile one file and get parent dir
diff --git a/vlib/compiler/parser.v b/vlib/compiler/parser.v
index df291faaa6..8f3fa00a2d 100644
--- a/vlib/compiler/parser.v
+++ b/vlib/compiler/parser.v
@@ -2137,7 +2137,10 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 		// }
 		if is_indexer {
 			l := p.cgen.cur_line.trim_space()
-			index_val := l[l.last_index(' ')..].trim_space()
+			idx := l.last_index(' ') or {
+				panic('idx')
+			}
+			index_val := l[idx..].trim_space()
 			p.cgen.resetln(l[..fn_ph])
 			p.table.varg_access << VargAccess{
 				fn_name: p.cur_fn.name,
diff --git a/vlib/net/urllib/urllib.v b/vlib/net/urllib/urllib.v
index 3745c7ab50..5f6c262435 100644
--- a/vlib/net/urllib/urllib.v
+++ b/vlib/net/urllib/urllib.v
@@ -551,7 +551,7 @@ struct ParseAuthorityRes {
 }
 
 fn parse_authority(authority string) ?ParseAuthorityRes {
-	i := authority.last_index('@')
+	i := authority.last_index('@') or { -1 }
 	mut host := ''
 	mut zuser := user('')
 	if i < 0 {
@@ -602,8 +602,7 @@ fn parse_host(host string) ?string {
 	if host.starts_with('[') {
 		// parse an IP-Literal in RFC 3986 and RFC 6874.
 		// E.g., '[fe80::1]', '[fe80::1%25en0]', '[fe80::1]:80'.
-		mut i := host.last_index(']')
-		if i < 0 {
+		mut i := host.last_index(']') or {
 			return error(error_msg('parse_host: missing \']\' in host', ''))
 		}
 		mut colon_port := host[i+1..]
@@ -629,9 +628,8 @@ fn parse_host(host string) ?string {
 			}
 			return host1 + host2 + host3
 		}
-		i = host.last_index(':')
-		if i != -1 {
-			colon_port = host[i..]
+		if idx := host.last_index(':')  {
+			colon_port = host[idx..]
 			if !valid_optional_port(colon_port) {
 				return error(error_msg('parse_host: invalid port $colon_port after host ', ''))
 			}
@@ -910,7 +908,7 @@ fn resolve_path(base, ref string) string {
 	if ref == '' {
 		full = base
 	} else if ref[0] != `/` {
-		i := base.last_index('/')
+		i := base.last_index('/') or { -1 }
 		full = base[..i+1] + ref
 	} else {
 		full = ref
diff --git a/vlib/os/os.v b/vlib/os/os.v
index 2144af8d68..1bff1bf629 100644
--- a/vlib/os/os.v
+++ b/vlib/os/os.v
@@ -569,8 +569,7 @@ fn print_c_errno() {
 
 
 pub fn ext(path string) string {
-	pos := path.last_index('.')
-	if pos == -1 {
+	pos := path.last_index('.') or {
 		return ''
 	}
 	return path[pos..]
@@ -582,16 +581,14 @@ pub fn dir(path string) string {
 	if path == '.' {
 		return getwd()
 	}
-	pos := path.last_index(path_separator)
-	if pos == -1 {
+	pos := path.last_index(path_separator) or {
 		return '.'
 	}
 	return path[..pos]
 }
 
 fn path_sans_ext(path string) string {
-	pos := path.last_index('.')
-	if pos == -1 {
+	pos := path.last_index('.') or {
 		return path
 	}
 	return path[..pos]
@@ -599,8 +596,7 @@ fn path_sans_ext(path string) string {
 
 
 pub fn basedir(path string) string {
-	pos := path.last_index(path_separator)
-	if pos == -1 {
+	pos := path.last_index(path_separator) or {
 		return path
 	}
 	return path[..pos ] // NB: *without* terminating /