diff --git a/csrc/trtllm_fused_moe_dev_kernel.cu b/csrc/trtllm_fused_moe_dev_kernel.cu
index ead183cfd2..63e8aef5a4 100644
--- a/csrc/trtllm_fused_moe_dev_kernel.cu
+++ b/csrc/trtllm_fused_moe_dev_kernel.cu
@@ -78,7 +78,8 @@ __global__ void activationKernel(KernelParams params) {
       // Loop over hidden dim
       for (int hiddenIdx = threadIdx.x + blockDim.x * blockIdx.x; hiddenIdx < params.innerDim / 2;
            hiddenIdx += blockDim.x * gridDim.x) {
-        int const baseIdx = permutedIdx * params.innerDim + hiddenIdx;
+        // Use int64_t to avoid overflow when permutedIdx * innerDim > INT32_MAX
+        int64_t const baseIdx = (int64_t)permutedIdx * params.innerDim + hiddenIdx;
 
         float x1 = (float)params.inPtr[baseIdx];
         float x2 = (float)params.inPtr[baseIdx + params.innerDim / 2];
@@ -86,7 +87,7 @@ __global__ void activationKernel(KernelParams params) {
         float act = silu(x2);
         Type out = (Type)(act * x1);
 
-        int const outIdx = permutedIdx * (params.innerDim / 2) + hiddenIdx;
+        int64_t const outIdx = (int64_t)permutedIdx * (params.innerDim / 2) + hiddenIdx;
         params.outPtr[outIdx] = out;
       }
     }
@@ -261,11 +262,14 @@ __global__ void activationDeepSeekKernel(KernelParams params) {
           }
 
           // Process blocks for this CTA
-          int const baseIdx = permutedIdx * params.innerDim + hiddenIdx;
+          // Use int64_t to avoid overflow when permutedIdx * innerDim > INT32_MAX
+          int64_t const baseIdx = (int64_t)permutedIdx * params.innerDim + hiddenIdx;
 
-          int const scale1Idx = permutedIdx + totalNumPaddedTokens * (hiddenIdx / 128);
-          int const scale2Idx = permutedIdx + totalNumPaddedTokens *
-                                                  ((hiddenIdx / 128) + (params.innerDim / 2 / 128));
+          int64_t const scale1Idx =
+              (int64_t)permutedIdx + (int64_t)totalNumPaddedTokens * (hiddenIdx / 128);
+          int64_t const scale2Idx =
+              (int64_t)permutedIdx +
+              (int64_t)totalNumPaddedTokens * ((hiddenIdx / 128) + (params.innerDim / 2 / 128));
 
           scale1Arr[tokenInCtaIdx] = params.inDqSfsPtr[scale1Idx];
           scale2Arr[tokenInCtaIdx] = params.inDqSfsPtr[scale2Idx];
@@ -304,8 +308,8 @@ __global__ void activationDeepSeekKernel(KernelParams params) {
             float scaleOut =
                 fmaxf(aMaxArr[tokenInCtaIdx] / E4m3MaxVal, std::numeric_limits<float>::min());
             s_scaleOutArr[tokenInCtaIdx] = scaleOut;
-            int const scaleOut_idx =
-                permutedIdxArr[tokenInCtaIdx] + totalNumPaddedTokens * (hiddenIdx / 128);
+            int64_t const scaleOut_idx = (int64_t)permutedIdxArr[tokenInCtaIdx] +
+                                         (int64_t)totalNumPaddedTokens * (hiddenIdx / 128);
             params.outDqSfsPtr[scaleOut_idx] = scaleOut;
           }
         }
@@ -322,7 +326,7 @@ __global__ void activationDeepSeekKernel(KernelParams params) {
             continue;
           }
           float const scaleOut = s_scaleOutArr[tokenInCtaIdx];
-          int const outIdx = permutedIdx * (params.innerDim / 2) + hiddenIdx;
+          int64_t const outIdx = (int64_t)permutedIdx * (params.innerDim / 2) + hiddenIdx;
           params.outPtr[outIdx] = static_cast<Type>(outArr[tokenInCtaIdx] / scaleOut);
         }
       }