diff --git a/src/nyx/features/3d_ngldm.cpp b/src/nyx/features/3d_ngldm.cpp
index 52532f0d..fa5c8145 100644
--- a/src/nyx/features/3d_ngldm.cpp
+++ b/src/nyx/features/3d_ngldm.cpp
@@ -305,17 +305,22 @@ void D3_NGLDM_feature::calc_features(const std::vector<double>& Sg, const std::v
 		f_GLNUN += sj * sj;	// Grey Level Non Uniformity Normalised
 	}
 
-	for (int i = 0; i < Ng; ++i)
+	// FIX (bug): DCNU/DCNUN summed the GREY-LEVEL (row) marginal s_{i.}=sum_j s_ij (outer loop over i,
+	// inner sum over j) -- byte-identical to the GLNU loop above, so DCNU==GLNU always. DCNU is the
+	// DEPENDENCE-COUNT (column) marginal: s_{.j}=sum_i s_ij, then sum_j s_{.j}^2. Transpose the loops
+	// (outer over dependence-count columns j, inner sum over grey levels i), matching the row-marginal's
+	// j in [1,Nr) convention. (The 2D twin ngldm.cpp is already correct via separate Sg/Sr arrays.)
+	for (int j = 1; j < Nr; ++j)	// FIX: outer loop is now the dependence-count column j
 	{
-		// Aggregate nonzero dependencies at each grey level
-		double si = 0;
-		for (int j = 1; j < Nr; ++j)	// note: j \in [1,Nr) due to considering only nonzero dependencies
+		// Aggregate over grey levels at each dependence count
+		double scol = 0;	// FIX: column marginal s_{.j}
+		for (int i = 0; i < Ng; ++i)	// FIX: sum over grey levels i
 		{
 			double sij = NGLDM.yx(i, j);
-			si += sij;
+			scol += sij;
 		}
-		f_DCNU += si * si;	// Dependence Count Non Uniformity
-		f_DCNUN += si * si;	// Dependence Count Non Uniformity Normalised 
+		f_DCNU += scol * scol;	// FIX: Dependence Count Non Uniformity = sum_j s_{.j}^2
+		f_DCNUN += scol * scol;	// FIX: Dependence Count Non Uniformity Normalised
 	}
 
 	for (int i = 0; i < Ng; ++i)
diff --git a/tests/test_3d_coverage_common.h b/tests/test_3d_coverage_common.h
index 248caf30..111a8480 100644
--- a/tests/test_3d_coverage_common.h
+++ b/tests/test_3d_coverage_common.h
@@ -392,8 +392,8 @@ static const std::map<std::string, std::vector<double>>& unvetted_3d_local_regre
 		{ "3NGLDM_DCENE", { 0.14348407632898436 } },
 		{ "3NGLDM_DCENT", { 5.2277449211654039 } },
 		{ "3NGLDM_DCM", { 13.485998122653307 } },
-		{ "3NGLDM_DCNU", { 115443.18172715895 } },
-		{ "3NGLDM_DCNUN", { 0.22575716076180957 } },
+		{ "3NGLDM_DCNU", { 85056.840050062572 } },   // FIXED: was 115443.18172715895 (== GLNU, a transposed-marginal bug in 3d_ngldm.cpp)
+		{ "3NGLDM_DCNUN", { 0.16633455892143026 } }, // FIXED: was 0.22575716076180957 (== GLNUN, same bug)
 		{ "3NGLDM_DCP", { 1 } },
 		{ "3NGLDM_DCV", { 86.17064428912758 } },
 		{ "3NGLDM_GLM", { 16.955115769712151 } },
diff --git a/tests/test_3d_ngldm_ibsi.h b/tests/test_3d_ngldm_ibsi.h
index 75a3340b..00e61f66 100644
--- a/tests/test_3d_ngldm_ibsi.h
+++ b/tests/test_3d_ngldm_ibsi.h
@@ -18,8 +18,8 @@ static std::unordered_map<std::string, double> d3ngldm_GT{
 		{ "3NGLDM_HDHGLE",	20030.0 },
 		{ "3NGLDM_GLNU",	115443.0 },
 		{ "3NGLDM_GLNUN",	0.23 },
-		{ "3NGLDM_DCNU",	115443.0 },
-		{ "3NGLDM_DCNUN",	0.23 },
+		{ "3NGLDM_DCNU",	85056.8 },   // FIXED: was 115443 (== GLNU) -- transposed-marginal bug in 3d_ngldm.cpp
+		{ "3NGLDM_DCNUN",	0.166335 },  // FIXED: was 0.23 (== GLNUN), same bug
 		{ "3NGLDM_DCP",	1.0 },
 		{ "3NGLDM_GLM",	17.0 },
 		{ "3NGLDM_GLV",	190.0 },