diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 1638b0fd9..0b038a56d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -333,7 +333,7 @@ jobs:
         run: nix build .#ghostty-releasefast
 
       - name: Check version
-        run: result/bin/ghostty +version | grep -q 'builtin.OptimizeMode.ReleaseFast'
+        run: result/bin/ghostty +version | grep -q '.ReleaseFast'
 
       - name: Check to see if the binary has been stripped
         run: nm result/bin/.ghostty-wrapped 2>&1 | grep -q 'no symbols'
@@ -342,7 +342,7 @@ jobs:
         run: nix build .#ghostty-debug
 
       - name: Check version
-        run: result/bin/ghostty +version | grep -q 'builtin.OptimizeMode.Debug'
+        run: result/bin/ghostty +version | grep -q '.Debug'
 
       - name: Check to see if the binary has not been stripped
         run: nm result/bin/.ghostty-wrapped 2>&1 | grep -q 'main_ghostty.main'
@@ -513,7 +513,7 @@ jobs:
           $fileContent = Get-Content -Path "build.zig" -Raw
           $pattern = 'buildpkg\.requireZig\("(.*?)"\);'
           $zigVersion = [regex]::Match($fileContent, $pattern).Groups[1].Value
-          $version = "zig-windows-x86_64-$zigVersion"
+          $version = "zig-x86_64-windows-$zigVersion"
           Write-Output $version
           $uri = "https://ziglang.org/download/$zigVersion/$version.zip"
           Invoke-WebRequest -Uri "$uri" -OutFile ".\zig-windows.zip"
diff --git a/nix/package.nix b/nix/package.nix
index fcc80b9dc..73d31c3b9 100644
--- a/nix/package.nix
+++ b/nix/package.nix
@@ -10,7 +10,7 @@
   git,
   ncurses,
   pkg-config,
-  zig_0_14,
+  zig_0_15,
   pandoc,
   revision ? "dirty",
   optimize ? "Debug",
@@ -27,7 +27,7 @@
   # https://github.com/ziglang/zig/issues/14281#issuecomment-1624220653 is
   # ultimately acted on and has made its way to a nixpkgs implementation, this
   # can probably be removed in favor of that.
-  zig_hook = zig_0_14.hook.overrideAttrs {
+  zig_hook = zig_0_15.hook.overrideAttrs {
     zig_default_flags = "-Dcpu=baseline -Doptimize=${optimize} --color off";
   };
   gi_typelib_path = import ./build-support/gi-typelib-path.nix {
diff --git a/src/build/GhosttyLib.zig b/src/build/GhosttyLib.zig
index d5ec66de8..2ac383544 100644
--- a/src/build/GhosttyLib.zig
+++ b/src/build/GhosttyLib.zig
@@ -82,6 +82,9 @@ pub fn initShared(
             .omit_frame_pointer = deps.config.strip,
             .unwind_tables = if (deps.config.strip) .none else .sync,
         }),
+
+        // Fails on self-hosted x86_64
+        .use_llvm = true,
     });
     _ = try deps.add(lib);
 
diff --git a/src/build/docker/debian/Dockerfile b/src/build/docker/debian/Dockerfile
index 73c7da7c8..815d395cd 100644
--- a/src/build/docker/debian/Dockerfile
+++ b/src/build/docker/debian/Dockerfile
@@ -29,10 +29,10 @@ COPY ./build.zig /src
 # Install zig
 # https://ziglang.org/download/
 
-RUN export ZIG_VERSION=$(sed -n -e 's/^.*requireZig("\(.*\)").*$/\1/p' build.zig) && curl -L -o /tmp/zig.tar.xz "https://ziglang.org/download/$ZIG_VERSION/zig-linux-$(uname -m)-$ZIG_VERSION.tar.xz" && \
+RUN export ZIG_VERSION=$(sed -n -e 's/^.*requireZig("\(.*\)").*$/\1/p' build.zig) && curl -L -o /tmp/zig.tar.xz "https://ziglang.org/download/$ZIG_VERSION/zig-$(uname -m)-linux-$ZIG_VERSION.tar.xz" && \
     tar -xf /tmp/zig.tar.xz -C /opt && \
     rm /tmp/zig.tar.xz && \
-    ln -s "/opt/zig-linux-$(uname -m)-$ZIG_VERSION/zig" /usr/local/bin/zig
+    ln -s "/opt/zig-$(uname -m)-linux-$ZIG_VERSION/zig" /usr/local/bin/zig
 
 COPY . /src
 
diff --git a/src/font/Collection.zig b/src/font/Collection.zig
index e91fe03ae..5ec076608 100644
--- a/src/font/Collection.zig
+++ b/src/font/Collection.zig
@@ -223,12 +223,13 @@ fn getFaceFromEntry(
 
             // Calculate the scale factor for this
             // entry now that we have a loaded face.
-            entry.scale_factor = .{
-                .scale = self.scaleFactor(
+            if (entry.scale_factor == .adjustment) {
+                const factor = self.scaleFactor(
                     face.getMetrics(),
                     entry.scale_factor.adjustment,
-                ),
-            };
+                );
+                entry.scale_factor = .{ .scale = factor };
+            }
 
             // If our scale factor is something other
             // than 1.0 then we need to resize the face.
diff --git a/src/synthetic/cli/Ascii.zig b/src/synthetic/cli/Ascii.zig
index 14de5edb8..339bdee2e 100644
--- a/src/synthetic/cli/Ascii.zig
+++ b/src/synthetic/cli/Ascii.zig
@@ -35,10 +35,10 @@ pub fn run(self: *Ascii, writer: *std.Io.Writer, rand: std.Random) !void {
     while (true) {
         const data = try gen.next(&buf);
         writer.writeAll(data) catch |err| {
-            const Error = error{ NoSpaceLeft, BrokenPipe } || @TypeOf(err);
+            const Error = error{ WriteFailed, BrokenPipe } || @TypeOf(err);
             switch (@as(Error, err)) {
                 error.BrokenPipe => return, // stdout closed
-                error.NoSpaceLeft => return, // fixed buffer full
+                error.WriteFailed => return, // fixed buffer full
                 else => return err,
             }
         };
@@ -56,8 +56,6 @@ test Ascii {
     const rand = prng.random();
 
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
-    const writer = fbs.writer();
-
-    try impl.run(writer, rand);
+    var writer: std.Io.Writer = .fixed(&buf);
+    try impl.run(&writer, rand);
 }
diff --git a/src/synthetic/cli/Osc.zig b/src/synthetic/cli/Osc.zig
index 8dd3d46ed..23d19e4ae 100644
--- a/src/synthetic/cli/Osc.zig
+++ b/src/synthetic/cli/Osc.zig
@@ -39,10 +39,10 @@ pub fn run(self: *Osc, writer: *std.Io.Writer, rand: std.Random) !void {
     while (true) {
         const data = try gen.next(&buf);
         writer.writeAll(data) catch |err| {
-            const Error = error{ NoSpaceLeft, BrokenPipe } || @TypeOf(err);
+            const Error = error{ WriteFailed, BrokenPipe } || @TypeOf(err);
             switch (@as(Error, err)) {
                 error.BrokenPipe => return, // stdout closed
-                error.NoSpaceLeft => return, // fixed buffer full
+                error.WriteFailed => return, // fixed buffer full
                 else => return err,
             }
         };
@@ -60,8 +60,6 @@ test Osc {
     const rand = prng.random();
 
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
-    const writer = fbs.writer();
-
-    try impl.run(writer, rand);
+    var writer: std.Io.Writer = .fixed(&buf);
+    try impl.run(&writer, rand);
 }
diff --git a/src/synthetic/cli/Utf8.zig b/src/synthetic/cli/Utf8.zig
index 65437d1ae..3c2fddef7 100644
--- a/src/synthetic/cli/Utf8.zig
+++ b/src/synthetic/cli/Utf8.zig
@@ -34,10 +34,10 @@ pub fn run(self: *Utf8, writer: *std.Io.Writer, rand: std.Random) !void {
     while (true) {
         const data = try gen.next(&buf);
         writer.writeAll(data) catch |err| {
-            const Error = error{ NoSpaceLeft, BrokenPipe } || @TypeOf(err);
+            const Error = error{ WriteFailed, BrokenPipe } || @TypeOf(err);
             switch (@as(Error, err)) {
                 error.BrokenPipe => return, // stdout closed
-                error.NoSpaceLeft => return, // fixed buffer full
+                error.WriteFailed => return, // fixed buffer full
                 else => return err,
             }
         };
@@ -55,8 +55,6 @@ test Utf8 {
     const rand = prng.random();
 
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
-    const writer = fbs.writer();
-
-    try impl.run(writer, rand);
+    var writer: std.Io.Writer = .fixed(&buf);
+    try impl.run(&writer, rand);
 }
diff --git a/src/terminal/kitty/graphics_command.zig b/src/terminal/kitty/graphics_command.zig
index 08b2e378a..99a7cdaac 100644
--- a/src/terminal/kitty/graphics_command.zig
+++ b/src/terminal/kitty/graphics_command.zig
@@ -1214,41 +1214,41 @@ test "all i32 values" {
 test "response: encode nothing without ID or image number" {
     const testing = std.testing;
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
+    var writer: std.Io.Writer = .fixed(&buf);
 
     var r: Response = .{};
-    try r.encode(fbs.writer());
-    try testing.expectEqualStrings("", fbs.getWritten());
+    try r.encode(&writer);
+    try testing.expectEqualStrings("", writer.buffered());
 }
 
 test "response: encode with only image id" {
     const testing = std.testing;
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
+    var writer: std.Io.Writer = .fixed(&buf);
 
     var r: Response = .{ .id = 4 };
-    try r.encode(fbs.writer());
-    try testing.expectEqualStrings("\x1b_Gi=4;OK\x1b\\", fbs.getWritten());
+    try r.encode(&writer);
+    try testing.expectEqualStrings("\x1b_Gi=4;OK\x1b\\", writer.buffered());
 }
 
 test "response: encode with only image number" {
     const testing = std.testing;
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
+    var writer: std.Io.Writer = .fixed(&buf);
 
     var r: Response = .{ .image_number = 4 };
-    try r.encode(fbs.writer());
-    try testing.expectEqualStrings("\x1b_GI=4;OK\x1b\\", fbs.getWritten());
+    try r.encode(&writer);
+    try testing.expectEqualStrings("\x1b_GI=4;OK\x1b\\", writer.buffered());
 }
 
 test "response: encode with image ID and number" {
     const testing = std.testing;
     var buf: [1024]u8 = undefined;
-    var fbs = std.io.fixedBufferStream(&buf);
+    var writer: std.Io.Writer = .fixed(&buf);
 
     var r: Response = .{ .id = 12, .image_number = 4 };
-    try r.encode(fbs.writer());
-    try testing.expectEqualStrings("\x1b_Gi=12,I=4;OK\x1b\\", fbs.getWritten());
+    try r.encode(&writer);
+    try testing.expectEqualStrings("\x1b_Gi=12,I=4;OK\x1b\\", writer.buffered());
 }
 
 test "delete range command 1" {
diff --git a/src/terminfo/Source.zig b/src/terminfo/Source.zig
index 6a068c906..91fee1ace 100644
--- a/src/terminfo/Source.zig
+++ b/src/terminfo/Source.zig
@@ -230,8 +230,8 @@ test "encode" {
 
     // Encode
     var buf: [1024]u8 = undefined;
-    var buf_stream = std.io.fixedBufferStream(&buf);
-    try src.encode(buf_stream.writer());
+    var writer: std.Io.Writer = .fixed(&buf);
+    try src.encode(&writer);
 
     const expected =
         "ghostty|xterm-ghostty|Ghostty,\n" ++
@@ -239,5 +239,5 @@ test "encode" {
         "\tccc@,\n" ++
         "\tcolors#256,\n" ++
         "\tbel=^G,\n";
-    try std.testing.expectEqualStrings(@as([]const u8, expected), buf_stream.getWritten());
+    try std.testing.expectEqualStrings(@as([]const u8, expected), writer.buffered());
 }
diff --git a/src/terminfo/ghostty.zig b/src/terminfo/ghostty.zig
index f96154c9b..6451836e7 100644
--- a/src/terminfo/ghostty.zig
+++ b/src/terminfo/ghostty.zig
@@ -391,7 +391,7 @@ pub const ghostty: Source = .{
 test "encode" {
     // Encode
     var buf: [1024 * 16]u8 = undefined;
-    var buf_stream = std.io.fixedBufferStream(&buf);
-    try ghostty.encode(buf_stream.writer());
-    try std.testing.expect(buf_stream.getWritten().len > 0);
+    var writer: std.Io.Writer = .fixed(&buf);
+    try ghostty.encode(&writer);
+    try std.testing.expect(writer.buffered().len > 0);
 }