diff --git a/overflow.zig b/overflow.zig
new file mode 100644
index 0000000..4cd0a5e
--- /dev/null
+++ b/overflow.zig
@@ -0,0 +1,4 @@
+test "integer overflow at compile time" {
+    const x: u8 = 255;
+    const y = x + 1;
+}
diff --git a/runtime_overflow.zig b/runtime_overflow.zig
new file mode 100644
index 0000000..082f96a
--- /dev/null
+++ b/runtime_overflow.zig
@@ -0,0 +1,4 @@
+test "integer overflow at runtime" {
+    var x: u8 = 255;
+    x += 1;
+}
diff --git a/undefined.zig b/undefined.zig
new file mode 100644
index 0000000..7ba1938
--- /dev/null
+++ b/undefined.zig
@@ -0,0 +1,15 @@
+const std = @import("std");
+
+pub fn main() void {
+    // if you remove this line, the program does not compile because it detects
+    // the overflow at compile time. A little confusing that it's not
+    // @setCompileTimeSafety but that's ok.
+    @setRuntimeSafety(false);
+
+    var x: u8 = 255;
+    x += 1; // <-- this is an overflow
+
+    // this prints 0 on my machine but is apparently undefined. I wonder what
+    // it prints on other machines?
+    std.debug.print("X: {}\n", .{x});
+}