diff --git a/Source/astcenc_compress_symbolic.cpp b/Source/astcenc_compress_symbolic.cpp
index 98d24951..eb4fc917 100644
--- a/Source/astcenc_compress_symbolic.cpp
+++ b/Source/astcenc_compress_symbolic.cpp
@@ -368,8 +368,9 @@ static float compress_symbolic_block_for_partition_1plane(
 
 	int max_weight_quant = astc::min(static_cast<int>(QUANT_32), quant_limit);
 
+	bool is_hdr = (config.profile == ASTCENC_PRF_HDR) || (config.profile == ASTCENC_PRF_HDR_RGB_LDR_A);
 	auto compute_difference = &compute_symbolic_block_difference_1plane;
-	if ((partition_count == 1) && !(config.flags & ASTCENC_FLG_MAP_RGBM))
+	if ((partition_count == 1) && !(config.flags & ASTCENC_FLG_MAP_RGBM) && !is_hdr)
 	{
 		compute_difference = &compute_symbolic_block_difference_1plane_1partition;
 	}
diff --git a/Source/astcenc_decompress_symbolic.cpp b/Source/astcenc_decompress_symbolic.cpp
index e7791eef..91e6b444 100644
--- a/Source/astcenc_decompress_symbolic.cpp
+++ b/Source/astcenc_decompress_symbolic.cpp
@@ -354,6 +354,7 @@ float compute_symbolic_block_difference_2plane(
 	                       ep0, ep1);
 
 	vmask4 u8_mask = get_u8_component_mask(config.profile, blk);
+	bool any_lns = rgb_lns || a_lns;
 
 	// Unpack and compute error for each texel in the partition
 	unsigned int texel_count = bsd.texel_count;
@@ -395,11 +396,20 @@ float compute_symbolic_block_difference_2plane(
 			);
 		}
 
-		vfloat4 error = oldColor - color;
-		error = min(abs(error), 1e15f);
-		error = error * error;
+		// Compute sum of squared errors, weighted by channel weight
+		vfloat4 error = (oldColor - color);
+		error = dot(error, error * blk.channel_weight);
 
-		summa += min(dot(error, blk.channel_weight), ERROR_CALC_DEFAULT);
+		// Convert this relative sum of squared error for HDR to avoid light
+		// channels dominating the error calculations.
+		// See https://fgiesen.wordpress.com/2024/11/14/mrsse/
+		if (any_lns)
+		{
+			// TODO: Divisor could be precomputed at load time
+			error = error / (dot(oldColor, oldColor) + 1e-10f);
+		}
+
+		summa += min(error, ERROR_CALC_DEFAULT);
 	}
 
 	return summa.lane<0>();
@@ -451,6 +461,8 @@ float compute_symbolic_block_difference_1plane(
 		                       rgb_lns, a_lns,
 		                       ep0, ep1);
 
+		bool any_lns = rgb_lns || a_lns;
+
 		// Unpack and compute error for each texel in the partition
 		unsigned int texel_count = pi.partition_texel_count[i];
 		for (unsigned int j = 0; j < texel_count; j++)
@@ -492,11 +504,20 @@ float compute_symbolic_block_difference_1plane(
 				);
 			}
 
-			vfloat4 error = oldColor - color;
-			error = min(abs(error), 1e15f);
-			error = error * error;
+			// Compute sum of squared errors, weighted by channel weight
+			vfloat4 error = (oldColor - color);
+			error = dot(error, error * blk.channel_weight);
+
+			// Convert this relative sum of squared error for HDR to avoid light
+			// channels dominating the error calculations
+			// See https://fgiesen.wordpress.com/2024/11/14/mrsse/
+			if (any_lns)
+			{
+				// TODO: Divisor could be precomputed at load time
+				error = error / (dot(oldColor, oldColor) + 1e-10f);
+			}
 
-			summa += min(dot(error, blk.channel_weight), ERROR_CALC_DEFAULT);
+			summa += min(error, ERROR_CALC_DEFAULT);
 		}
 	}