diff --git a/lib/std/mem.zig b/lib/std/mem.zig
index f263b3e851..fc0c226894 100644
--- a/lib/std/mem.zig
+++ b/lib/std/mem.zig
@@ -1346,6 +1346,7 @@ pub fn lastIndexOfLinear(comptime T: type, haystack: []const T, needle: []const
 /// Consider using `indexOfPos` instead of this, which will automatically use a
 /// more sophisticated algorithm on larger inputs.
 pub fn indexOfPosLinear(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
+    if (needle.len > haystack.len) return null;
     var i: usize = start_index;
     const end = haystack.len - needle.len;
     while (i <= end) : (i += 1) {
@@ -1354,6 +1355,26 @@ pub fn indexOfPosLinear(comptime T: type, haystack: []const T, start_index: usiz
     return null;
 }
 
+test indexOfPosLinear {
+    try testing.expectEqual(0, indexOfPosLinear(u8, "", 0, ""));
+    try testing.expectEqual(0, indexOfPosLinear(u8, "123", 0, ""));
+
+    try testing.expectEqual(null, indexOfPosLinear(u8, "", 0, "1"));
+    try testing.expectEqual(0, indexOfPosLinear(u8, "1", 0, "1"));
+    try testing.expectEqual(null, indexOfPosLinear(u8, "2", 0, "1"));
+    try testing.expectEqual(1, indexOfPosLinear(u8, "21", 0, "1"));
+    try testing.expectEqual(null, indexOfPosLinear(u8, "222", 0, "1"));
+
+    try testing.expectEqual(null, indexOfPosLinear(u8, "", 0, "12"));
+    try testing.expectEqual(null, indexOfPosLinear(u8, "1", 0, "12"));
+    try testing.expectEqual(null, indexOfPosLinear(u8, "2", 0, "12"));
+    try testing.expectEqual(0, indexOfPosLinear(u8, "12", 0, "12"));
+    try testing.expectEqual(null, indexOfPosLinear(u8, "21", 0, "12"));
+    try testing.expectEqual(1, indexOfPosLinear(u8, "212", 0, "12"));
+    try testing.expectEqual(0, indexOfPosLinear(u8, "122", 0, "12"));
+    try testing.expectEqual(1, indexOfPosLinear(u8, "212112", 0, "12"));
+}
+
 fn boyerMooreHorspoolPreprocessReverse(pattern: []const u8, table: *[256]usize) void {
     for (table) |*c| {
         c.* = pattern.len;