diff --git a/client/client_send.js b/client/client_send.js
index fd4b826..5ce8b83 100644
--- a/client/client_send.js
+++ b/client/client_send.js
@@ -8,7 +8,7 @@ function serializer_create(size) {
         'strview': new Uint8Array(buffer),
 
         'need_gpu_allocate': true, // need to call glBufferData to create a GPU buffer of size serializer.size
-        'gpu_upload_from': 0,      // need to call glBufferSubData for bytes in [serializer.gpu_upload_from, serializer.offset)
+        'gpu_upload_from': 0,      // need to call glBufferSubData/glTexSubImage2D for bytes in [serializer.gpu_upload_from, serializer.offset)
     };
 }
 
diff --git a/client/webgl_draw.js b/client/webgl_draw.js
index 479d819..06faa1a 100644
--- a/client/webgl_draw.js
+++ b/client/webgl_draw.js
@@ -25,26 +25,46 @@ function upload_if_needed(gl, buffer_kind, serializer) {
 }
 
 function upload_square_rgba16ui_texture(gl, serializer, texture_size) {
-    // TODO: only subupload what's needed
-
     const bpp = 2 * 4;
-    const data_size = serializer.offset;
-    const data_pixels = data_size / bpp; // data_size % bpp is expected to always be zero here
+    const data_size = serializer.offset - serializer.gpu_upload_from;
+
+    let data_pixels = data_size / bpp; // data_size % bpp is expected to always be zero here
+
+    const pixels_already_uploaded = serializer.gpu_upload_from / bpp;
+    let rows_uploaded = Math.floor(pixels_already_uploaded / texture_size);
+    const rows_remainder = pixels_already_uploaded % texture_size;
+
+    // Upload first non-whole row (if last upload was not a whole number of rows)
+    if (rows_remainder > 0) {
+        const row_upload_to_full = texture_size - rows_remainder;
+        const first_upload = Math.min(row_upload_to_full, data_pixels);
+
+        if (first_upload > 0) {
+            gl.texSubImage2D(gl.TEXTURE_2D, 0, rows_remainder, rows_uploaded, first_upload, 1, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(serializer.buffer, serializer.gpu_upload_from, first_upload * 4));
+
+            data_pixels -= first_upload;
+            serializer.gpu_upload_from += first_upload;
+            rows_uploaded += 1;
+        }
+    }
 
     const rows = Math.ceil(data_pixels / texture_size);
     const last_row = data_pixels % texture_size;
-    const whole_upload = (rows - 1) * texture_size * bpp;
+    const whole_upload = (rows - 1) * texture_size;
 
     // Upload whole rows
     if (rows > 1) {
-        gl.texSubImage2D(gl.TEXTURE_2D, 0, 0, 0, texture_size, rows - 1, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(serializer.buffer, 0, whole_upload / 2));
+        gl.texSubImage2D(gl.TEXTURE_2D, 0, 0, rows_uploaded, texture_size, rows - 1, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(serializer.buffer, serializer.gpu_upload_from, whole_upload * 4));
+        rows_uploaded += rows - 1;
     }
 
     // Upload last row
-    if (last_row > 0) {        
+    if (last_row > 0) {  
         const last_row_upload = last_row * bpp;
-        gl.texSubImage2D(gl.TEXTURE_2D, 0, 0, rows - 1, last_row, 1, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(serializer.buffer, whole_upload, last_row_upload / 2));
+        gl.texSubImage2D(gl.TEXTURE_2D, 0, 0, rows_uploaded, last_row, 1, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(serializer.buffer, whole_upload, last_row_upload * 4));
     }
+
+    serializer.gpu_upload_from = serializer.offset;
 }
 
 function draw_html(state) {