diff --git a/projects/common/src/client/java/dan200/computercraft/client/integration/IrisShaderMod.java b/projects/common/src/client/java/dan200/computercraft/client/integration/IrisShaderMod.java
index 85581bb84..1a6b33bae 100644
--- a/projects/common/src/client/java/dan200/computercraft/client/integration/IrisShaderMod.java
+++ b/projects/common/src/client/java/dan200/computercraft/client/integration/IrisShaderMod.java
@@ -5,18 +5,16 @@
 package dan200.computercraft.client.integration;
 
 import com.google.auto.service.AutoService;
-import com.mojang.blaze3d.vertex.ByteBufferBuilder;
 import com.mojang.blaze3d.vertex.VertexFormat;
 import dan200.computercraft.client.render.text.DirectFixedWidthFontRenderer;
 import dan200.computercraft.shared.platform.PlatformHelper;
 import net.irisshaders.iris.api.v0.IrisApi;
 import net.irisshaders.iris.api.v0.IrisTextVertexSink;
 import net.minecraft.client.renderer.LightTexture;
-import org.jspecify.annotations.Nullable;
-import org.lwjgl.system.MemoryUtil;
 
 import java.nio.ByteBuffer;
 import java.util.Optional;
+import java.util.function.IntFunction;
 
 @AutoService(ShaderMod.Provider.class)
 public class IrisShaderMod implements ShaderMod.Provider {
@@ -32,21 +30,20 @@ public class IrisShaderMod implements ShaderMod.Provider {
         }
 
         @Override
-        public DirectFixedWidthFontRenderer.QuadEmitter getQuadEmitter(int vertexCount, ByteBufferBuilder makeBuffer) {
-            return IrisApi.getInstance().getMinorApiRevision() >= 1
-                ? new IrisQuadEmitter(vertexCount, makeBuffer)
-                : super.getQuadEmitter(vertexCount, makeBuffer);
+        public DirectFixedWidthFontRenderer.QuadEmitter getQuadEmitter(int quadCount, IntFunction<ByteBuffer> makeBuffer) {
+            return new IrisQuadEmitter(quadCount, makeBuffer);
         }
 
         private static final class IrisQuadEmitter extends DirectFixedWidthFontRenderer.QuadEmitter {
             private final IrisTextVertexSink sink;
-            private @Nullable ByteBuffer buffer;
 
-            private IrisQuadEmitter(int vertexCount, ByteBufferBuilder builder) {
-                sink = IrisApi.getInstance().createTextVertexSink(vertexCount, i -> {
-                    if (buffer != null) throw new IllegalStateException("Allocated multiple buffers");
-                    return buffer = MemoryUtil.memByteBuffer(builder.reserve(i), i);
-                });
+            private IrisQuadEmitter(int vertexCount, IntFunction<ByteBuffer> builder) {
+                sink = IrisApi.getInstance().createTextVertexSink(vertexCount, builder);
+            }
+
+            @Override
+            public ByteBuffer byteBuffer() {
+                return sink.getUnderlyingByteBuffer();
             }
 
             @Override
diff --git a/projects/common/src/client/java/dan200/computercraft/client/integration/ShaderMod.java b/projects/common/src/client/java/dan200/computercraft/client/integration/ShaderMod.java
index 6285229cc..b49f02464 100644
--- a/projects/common/src/client/java/dan200/computercraft/client/integration/ShaderMod.java
+++ b/projects/common/src/client/java/dan200/computercraft/client/integration/ShaderMod.java
@@ -4,11 +4,14 @@
 
 package dan200.computercraft.client.integration;
 
-import com.mojang.blaze3d.vertex.ByteBufferBuilder;
 import dan200.computercraft.client.render.text.DirectFixedWidthFontRenderer;
 
+import java.nio.ByteBuffer;
 import java.util.Optional;
 import java.util.ServiceLoader;
+import java.util.function.IntFunction;
+
+import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.TERMINAL_TEXT;
 
 /**
  * Find the currently loaded shader mod (if present) and provides utilities for interacting with it.
@@ -30,12 +33,12 @@ public class ShaderMod {
     /**
      * Get an appropriate quad emitter for use with a vertex buffer and {@link DirectFixedWidthFontRenderer} .
      *
-     * @param vertexCount The number of vertices.
-     * @param buffer      A function to allocate a temporary buffer.
+     * @param quadCount  The number of quads.
+     * @param makeBuffer A function to allocate a temporary buffer.
      * @return The quad emitter.
      */
-    public DirectFixedWidthFontRenderer.QuadEmitter getQuadEmitter(int vertexCount, ByteBufferBuilder buffer) {
-        return new DirectFixedWidthFontRenderer.ByteBufferEmitter(buffer);
+    public DirectFixedWidthFontRenderer.QuadEmitter getQuadEmitter(int quadCount, IntFunction<ByteBuffer> makeBuffer) {
+        return new DirectFixedWidthFontRenderer.ByteBufferEmitter(makeBuffer.apply(TERMINAL_TEXT.format().getVertexSize() * quadCount * 4));
     }
 
     public interface Provider {
diff --git a/projects/common/src/client/java/dan200/computercraft/client/render/monitor/MonitorBlockEntityRenderer.java b/projects/common/src/client/java/dan200/computercraft/client/render/monitor/MonitorBlockEntityRenderer.java
index 1d3bbef15..a6ea0649b 100644
--- a/projects/common/src/client/java/dan200/computercraft/client/render/monitor/MonitorBlockEntityRenderer.java
+++ b/projects/common/src/client/java/dan200/computercraft/client/render/monitor/MonitorBlockEntityRenderer.java
@@ -7,7 +7,6 @@ package dan200.computercraft.client.render.monitor;
 import com.mojang.blaze3d.buffers.BufferType;
 import com.mojang.blaze3d.buffers.BufferUsage;
 import com.mojang.blaze3d.systems.RenderSystem;
-import com.mojang.blaze3d.vertex.ByteBufferBuilder;
 import com.mojang.blaze3d.vertex.PoseStack;
 import com.mojang.math.Axis;
 import dan200.computercraft.annotations.ForgeOverride;
@@ -28,7 +27,10 @@ import net.minecraft.client.renderer.blockentity.BlockEntityRendererProvider;
 import net.minecraft.world.phys.AABB;
 import net.minecraft.world.phys.Vec3;
 import org.joml.Matrix4f;
+import org.jspecify.annotations.Nullable;
+import org.lwjgl.system.MemoryUtil;
 
+import java.nio.ByteBuffer;
 import java.util.OptionalDouble;
 import java.util.OptionalInt;
 
@@ -42,7 +44,7 @@ public class MonitorBlockEntityRenderer implements BlockEntityRenderer<MonitorBl
      */
     private static final float MARGIN = (float) (MonitorBlockEntity.RENDER_MARGIN * 1.1);
 
-    private static final ByteBufferBuilder backingBufferBuilder = new ByteBufferBuilder(0x4000);
+    private static @Nullable ByteBuffer backingBuffer;
 
     public MonitorBlockEntityRenderer(BlockEntityRendererProvider.Context context) {
     }
@@ -129,9 +131,9 @@ public class MonitorBlockEntityRenderer implements BlockEntityRenderer<MonitorBl
 
         if (redraw) {
             // Cursor, Foreground, Background+Margin
-            var maxVertexCount = 4 * (1 + (terminal.getWidth() * terminal.getHeight()) + ((terminal.getWidth() + 2) * (terminal.getHeight() + 2)));
-            backingBufferBuilder.clear();
-            var sink = ShaderMod.get().getQuadEmitter(maxVertexCount, backingBufferBuilder);
+            var maxQuadCount = 1 + (terminal.getWidth() * terminal.getHeight()) + ((terminal.getWidth() + 2) * (terminal.getHeight() + 2));
+            var maxVertexCount = 4 * maxQuadCount;
+            var sink = ShaderMod.get().getQuadEmitter(maxQuadCount, MonitorBlockEntityRenderer::getBuffer);
 
             DirectFixedWidthFontRenderer.drawTerminalBackground(sink, 0, 0, terminal, yMargin, yMargin, xMargin, xMargin);
             var vertexCountAfterBackground = sink.vertexCount();
@@ -146,39 +148,48 @@ public class MonitorBlockEntityRenderer implements BlockEntityRenderer<MonitorBl
                 throw new IllegalStateException("Drew too many vertices. Expected " + maxVertexCount + ", drew " + vertexCountAfterCursor);
             }
 
-            try (var result = backingBufferBuilder.build()) {
-                if (result == null) {
-                    // If we have nothing to draw, just mark it as empty. We'll skip drawing in drawWithShader.
-                    renderState.indexAfterBackground = renderState.indexAfterForeground = renderState.indexAfterCursor = 0;
-                } else {
-                    renderState.register();
+            final int indexAfterBackground, indexAfterForeground, indexAfterCursor;
+            if (vertexCountAfterCursor == 0) {
+                // If we have nothing to draw, just mark it as empty. We'll skip drawing in drawWithShader.
+                indexAfterBackground = indexAfterForeground = indexAfterCursor = 0;
+            } else {
+                renderState.register();
 
-                    var commandEncoder = RenderSystem.getDevice().createCommandEncoder();
+                var commandEncoder = RenderSystem.getDevice().createCommandEncoder();
 
-                    var resultBuffer = result.byteBuffer();
-                    if (resultBuffer.limit() / sink.format().getVertexSize() != vertexCountAfterCursor) {
-                        throw new IllegalStateException("Mismatched vertex count");
-                    }
+                var resultBuffer = sink.byteBuffer().flip();
 
-                    if (renderState.vertexBuffer == null || resultBuffer.limit() > renderState.vertexBuffer.size()) {
-                        if (renderState.vertexBuffer != null) {
-                            renderState.vertexBuffer.close();
-                            renderState.vertexBuffer = null;
-                        }
-                        renderState.vertexBuffer = RenderSystem.getDevice().createBuffer(
-                            () -> "Monitor at " + monitor.getOrigin().getBlockPos(),
-                            BufferType.VERTICES, BufferUsage.STATIC_WRITE, resultBuffer
-                        );
-                    } else if (!renderState.vertexBuffer.isClosed()) {
-                        commandEncoder.writeToBuffer(renderState.vertexBuffer, resultBuffer, 0);
-                    }
+                // Ensure our buffer contains the correct number of vertices.
+                if (resultBuffer.remaining() != sink.format().getVertexSize() * vertexCountAfterCursor) {
+                    throw new IllegalStateException(String.format(
+                        "Mismatched vertex count. Buffer is %d bytes long, but was expected to be %d (vertex size) * %d (vertex count) = %d bytes.",
+                        resultBuffer.limit(), sink.format().getVertexSize(), vertexCountAfterCursor, sink.format().getVertexSize() * vertexCountAfterCursor
+                    ));
                 }
+
+                // Upload the buffer, reallocating if required.
+                if (renderState.vertexBuffer == null || resultBuffer.remaining() > renderState.vertexBuffer.size()) {
+                    if (renderState.vertexBuffer != null) {
+                        renderState.vertexBuffer.close();
+                        renderState.vertexBuffer = null;
+                    }
+                    renderState.vertexBuffer = RenderSystem.getDevice().createBuffer(
+                        () -> "Monitor at " + monitor.getOrigin().getBlockPos(),
+                        BufferType.VERTICES, BufferUsage.STATIC_WRITE, resultBuffer
+                    );
+                } else if (!renderState.vertexBuffer.isClosed()) {
+                    commandEncoder.writeToBuffer(renderState.vertexBuffer, resultBuffer, 0);
+                }
+
+                var mode = FixedWidthFontRenderer.TERMINAL_TEXT.mode();
+                indexAfterBackground = mode.indexCount(vertexCountAfterBackground);
+                indexAfterForeground = mode.indexCount(vertexCountAfterForeground);
+                indexAfterCursor = mode.indexCount(vertexCountAfterCursor);
             }
 
-            var mode = FixedWidthFontRenderer.TERMINAL_TEXT.mode();
-            renderState.indexAfterBackground = mode.indexCount(vertexCountAfterBackground);
-            renderState.indexAfterForeground = mode.indexCount(vertexCountAfterForeground);
-            renderState.indexAfterCursor = mode.indexCount(vertexCountAfterCursor);
+            renderState.indexAfterForeground = indexAfterForeground;
+            renderState.indexAfterBackground = indexAfterBackground;
+            renderState.indexAfterCursor = indexAfterCursor;
         }
 
         if (renderState.indexAfterCursor == 0) return;
@@ -249,4 +260,14 @@ public class MonitorBlockEntityRenderer implements BlockEntityRenderer<MonitorBl
     public AABB getRenderBoundingBox(MonitorBlockEntity monitor) {
         return monitor.getRenderBoundingBox();
     }
+
+    private static ByteBuffer getBuffer(int capacity) {
+        var buffer = backingBuffer;
+        if (buffer == null || buffer.capacity() < capacity) {
+            buffer = backingBuffer = buffer == null ? MemoryUtil.memAlloc(capacity) : MemoryUtil.memRealloc(buffer, capacity);
+        }
+
+        buffer.clear();
+        return buffer;
+    }
 }
diff --git a/projects/common/src/client/java/dan200/computercraft/client/render/text/DirectFixedWidthFontRenderer.java b/projects/common/src/client/java/dan200/computercraft/client/render/text/DirectFixedWidthFontRenderer.java
index 50c865d88..db3eff6b4 100644
--- a/projects/common/src/client/java/dan200/computercraft/client/render/text/DirectFixedWidthFontRenderer.java
+++ b/projects/common/src/client/java/dan200/computercraft/client/render/text/DirectFixedWidthFontRenderer.java
@@ -4,7 +4,6 @@
 
 package dan200.computercraft.client.render.text;
 
-import com.mojang.blaze3d.vertex.ByteBufferBuilder;
 import com.mojang.blaze3d.vertex.DefaultVertexFormat;
 import com.mojang.blaze3d.vertex.VertexConsumer;
 import com.mojang.blaze3d.vertex.VertexFormat;
@@ -15,6 +14,7 @@ import dan200.computercraft.core.util.Colour;
 import net.minecraft.util.ARGB;
 import org.lwjgl.system.MemoryUtil;
 
+import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
 import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.*;
@@ -164,6 +164,8 @@ public final class DirectFixedWidthFontRenderer {
     public abstract static class QuadEmitter {
         private int vertexCount;
 
+        public abstract ByteBuffer byteBuffer();
+
         public abstract VertexFormat format();
 
         protected abstract void quad(float x1, float y1, float x2, float y2, float z, int colour, float u1, float v1, float u2, float v2);
@@ -174,10 +176,15 @@ public final class DirectFixedWidthFontRenderer {
     }
 
     public static final class ByteBufferEmitter extends QuadEmitter {
-        private final ByteBufferBuilder builder;
+        private final ByteBuffer buffer;
 
-        public ByteBufferEmitter(ByteBufferBuilder builder) {
-            this.builder = builder;
+        public ByteBufferEmitter(ByteBuffer buffer) {
+            this.buffer = buffer;
+        }
+
+        @Override
+        public ByteBuffer byteBuffer() {
+            return buffer;
         }
 
         @Override
@@ -187,17 +194,18 @@ public final class DirectFixedWidthFontRenderer {
 
         @Override
         public void quad(float x1, float y1, float x2, float y2, float z, int colour, float u1, float v1, float u2, float v2) {
-            DirectFixedWidthFontRenderer.quad(builder, x1, y1, x2, y2, z, colour, u1, v1, u2, v2);
+            DirectFixedWidthFontRenderer.quad(buffer, x1, y1, x2, y2, z, colour, u1, v1, u2, v2);
         }
     }
 
-    static void quad(ByteBufferBuilder builder, float x1, float y1, float x2, float y2, float z, int colour, float u1, float v1, float u2, float v2) {
+    private static void quad(ByteBuffer buffer, float x1, float y1, float x2, float y2, float z, int colour, float u1, float v1, float u2, float v2) {
         // Emit a single quad to our buffer. This uses Unsafe (well, LWJGL's MemoryUtil) to directly blit bytes to the
         // underlying buffer. This allows us to have a single bounds check up-front, rather than one for every write.
         // This provides significant performance gains, at the cost of well, using Unsafe.
         // Each vertex is 28 bytes, giving 112 bytes in total. Vertices are of the form (xyz:FFF)(abgr:BBBB)(uv1:FF)(uv2:SS),
         // which matches the POSITION_COLOR_TEX_LIGHTMAP vertex format.
-        var addr = builder.reserve(112);
+        var position = buffer.position();
+        var addr = MemoryUtil.memAddress(buffer);
 
         // We're doing terrible unsafe hacks below, so let's be really sure that what we're doing is reasonable.
         // Require the pointer to be aligned to a 32-bit boundary.
@@ -246,6 +254,9 @@ public final class DirectFixedWidthFontRenderer {
         memPutShort(addr + 108, (short) 0xF0);
         memPutShort(addr + 110, (short) 0xF0);
 
+        // Finally increment the position.
+        buffer.position(position + 112);
+
         // Well done for getting to the end of this method. I recommend you take a break and go look at cute puppies.
     }
 }