diff --git a/src/gallium/frontends/mediafoundation/encode.cpp b/src/gallium/frontends/mediafoundation/encode.cpp
index 995b486dfff..6b52a4d1724 100644
--- a/src/gallium/frontends/mediafoundation/encode.cpp
+++ b/src/gallium/frontends/mediafoundation/encode.cpp
@@ -592,6 +592,12 @@ CDX12EncHMFT::PrepareForEncode( IMFSample *pSample, LPDX12EncodeContext *ppDX12E
          num_output_buffers = m_EncoderCapabilities.m_uiMaxHWSupportedMaxSlices;
       }
 
+      // Minimum per-slice buffer size to prevent excessively small allocations.
+      // This is especially important in PIPE_SLICE_MODE_AUTO where num_output_buffers
+      // can be set to the maximum possible slices, leading to very small per-slice
+      // buffer sizes that may be insufficient for actual bitstream data.
+      const uint32_t min_slice_buffer_size = 256 * 1024; // 256KB
+
       pDX12EncodeContext->sliceNotificationMode = D3D12_VIDEO_ENCODER_COMPRESSED_BITSTREAM_NOTIFICATION_MODE_FULL_FRAME;
       if( m_bSliceGenerationModeSet && ( m_uiSliceGenerationMode > 0 ) &&
           ( num_output_buffers > 1 ) /* IHV driver requires > 1 slices */ )
@@ -604,7 +610,7 @@ CDX12EncHMFT::PrepareForEncode( IMFSample *pSample, LPDX12EncodeContext *ppDX12E
             // Be careful with the allocation size of slice buffers, when the number of slices is high
             // and we run in LowLatency = 0, we can start thrashing when trying to MakeResident lots
             // of big allocations in short amounts of time (num slices x num in flight frames)
-            templ.width0 = ( m_uiMaxOutputBitstreamSize / num_output_buffers );
+            templ.width0 = std::max( ( m_uiMaxOutputBitstreamSize / num_output_buffers ), min_slice_buffer_size );
          }
          else
          {