diff --git a/backends/vulkan/patterns/quantized_convolution.py b/backends/vulkan/patterns/quantized_convolution.py
index 93140e15341..9a6fb69bf87 100644
--- a/backends/vulkan/patterns/quantized_convolution.py
+++ b/backends/vulkan/patterns/quantized_convolution.py
@@ -226,6 +226,16 @@ def make_q8ta_conv2d_custom_op(
             sum_per_output_channel = (
                 weight_tensor.sum(dim=1).to(torch.int32).contiguous()
             )
+        # Pad weight sums to align OC to multiple of 4, matching the alignment
+        # applied to weight, weight_scales, and bias above. Without this, the
+        # GPU shader would read out-of-bounds when OC is not a multiple of 4.
+        oc = sum_per_output_channel.shape[0]
+        if oc % 4 != 0:
+            num_padding = 4 - (oc % 4)
+            sum_per_output_channel = torch.nn.functional.pad(
+                sum_per_output_channel, (0, num_padding)
+            ).contiguous()
+
         sums_name = qweight_tensor_name + "_sums"
         # Sanitize the name
         sums_name = sums_name.replace(".", "_")
diff --git a/backends/vulkan/test/custom_ops/test_q8ta_conv2d_pw.cpp b/backends/vulkan/test/custom_ops/test_q8ta_conv2d_pw.cpp
index 51095c649b6..6ce6671ec84 100644
--- a/backends/vulkan/test/custom_ops/test_q8ta_conv2d_pw.cpp
+++ b/backends/vulkan/test/custom_ops/test_q8ta_conv2d_pw.cpp
@@ -210,6 +210,28 @@ static std::vector<TestCase> generate_quantized_conv2d_pw_test_cases() {
   }
 
   std::vector<Conv2dConfig> configs = {
+      // OC < 4 cases to test edge cases with partial output channel blocks
+      {OutInChannels(1, 16),
+       InputSize2D(8, 8),
+       KernelSize(1, 1),
+       Stride(1, 1),
+       Padding(0, 0),
+       Dilation(1, 1),
+       1},
+      {OutInChannels(2, 16),
+       InputSize2D(8, 8),
+       KernelSize(1, 1),
+       Stride(1, 1),
+       Padding(0, 0),
+       Dilation(1, 1),
+       1},
+      {OutInChannels(3, 16),
+       InputSize2D(8, 8),
+       KernelSize(1, 1),
+       Stride(1, 1),
+       Padding(0, 0),
+       Dilation(1, 1),
+       1},
       // Pointwise convolutions: kernel size 1x1
       {OutInChannels(32, 3),
        InputSize2D(64, 64),
diff --git a/backends/vulkan/test/custom_ops/utils.cpp b/backends/vulkan/test/custom_ops/utils.cpp
index b23c288a58f..2a50e7b5ec1 100644
--- a/backends/vulkan/test/custom_ops/utils.cpp
+++ b/backends/vulkan/test/custom_ops/utils.cpp
@@ -2064,7 +2064,11 @@ void compute_weight_sums(
   auto& weight_sums_data = weight_sums.get_int32_data();
   auto& quantized_weight_data = quantized_weight.get_int8_data();
 
-  weight_sums_data.resize(out_features);
+  // Don't resize down - the buffer may be pre-allocated with aligned size.
+  // Only resize up if needed.
+  if (weight_sums_data.size() < static_cast<size_t>(out_features)) {
+    weight_sums_data.resize(out_features);
+  }
 
   // For each output feature, compute the sum of quantized weights
   for (int64_t out_f = 0; out_f < out_features; ++out_f) {