diff --git a/lib/compiler/Maker/Step/ConfigHeader.zig b/lib/compiler/Maker/Step/ConfigHeader.zig
index 5096c8e0e3340fc5d841b5ae1677297bfb40417f..9444d3a6171c2157d042ef3ca2d1dd4b16ee5517 100644
--- a/lib/compiler/Maker/Step/ConfigHeader.zig
+++ b/lib/compiler/Maker/Step/ConfigHeader.zig
@@ -177,16 +177,18 @@ fn renderAutoConfUndef(
     var line_index: u32 = 0;
     var line_it = std.mem.splitScalar(u8, contents, '\n');
     while (line_it.next()) |line| : (line_index += 1) {
+        const last_line = line_it.index == line_it.buffer.len;
+
         if (!std.mem.startsWith(u8, line, "#")) {
             try w.writeAll(line);
-            try w.writeByte('\n');
+            if (!last_line) try w.writeByte('\n');
             continue;
         }
         var it = std.mem.tokenizeAny(u8, line[1..], " \t\r");
         const undef = it.next().?;
         if (!std.mem.eql(u8, undef, "undef")) {
             try w.writeAll(line);
-            try w.writeByte('\n');
+            if (!last_line) try w.writeByte('\n');
             continue;
         }
         const name = it.next().?;
diff --git a/test/standalone/config_header/autoconf_undef/config.h b/test/standalone/config_header/autoconf_undef/config.h
index 3a649b0aca5576d75099906310d28ef049d50f4a..854cbfc9f7fe9e1ed1de0dbea6f25ea687ec4264 100644
--- a/test/standalone/config_header/autoconf_undef/config.h
+++ b/test/standalone/config_header/autoconf_undef/config.h
@@ -30,5 +30,3 @@ int foo();
 // non-#undef # lines pass through unchanged
 #define KEPT_DEFINE value
 #include <kept.h>
-// TODO: unexpected newline is being added here
-
diff --git a/test/standalone/config_header/autoconf_undef/config.h.in b/test/standalone/config_header/autoconf_undef/config.h.in
index 1a13ccf319a85432ff04916ac0145b23bf78a7d3..39b0ec734ede142c24327af6038c288cd4fe161a 100644
--- a/test/standalone/config_header/autoconf_undef/config.h.in
+++ b/test/standalone/config_header/autoconf_undef/config.h.in
@@ -29,4 +29,3 @@ int foo();
 // non-#undef # lines pass through unchanged
 #define KEPT_DEFINE value
 #include <kept.h>
-// TODO: unexpected newline is being added here