diff --git a/demo/tests.cpp b/demo/tests.cpp
index ac4848489..e87a5a349 100644
--- a/demo/tests.cpp
+++ b/demo/tests.cpp
@@ -1221,6 +1221,78 @@ static void simplifyLockFlags()
 	assert(memcmp(ib, expected, sizeof(expected)) == 0);
 }
 
+static void simplifyLockFlagsSeam()
+{
+	float vb[] = {
+	    0, 0, 0,
+	    0, 1, 0,
+	    0, 1, 0,
+	    0, 2, 0,
+	    1, 0, 0,
+	    1, 1, 0,
+	    1, 1, 0,
+	    1, 2, 0,
+	    2, 0, 0,
+	    2, 1, 0,
+	    2, 1, 0,
+	    2, 2, 0, // clang-format :-/
+	};
+
+	unsigned char lock0[12] = {
+	    1, 0, 0, 1,
+	    0, 0, 0, 0,
+	    1, 0, 0, 1, // clang-format :-/
+	};
+
+	unsigned char lock1[12] = {
+	    1, 0, 0, 1,
+	    1, 0, 0, 1,
+	    1, 0, 0, 1, // clang-format :-/
+	};
+
+	unsigned char lock2[12] = {
+	    1, 0, 1, 1,
+	    1, 0, 1, 1,
+	    1, 0, 1, 1, // clang-format :-/
+	};
+
+	unsigned char lock3[12] = {
+	    1, 1, 0, 1,
+	    1, 1, 0, 1,
+	    1, 1, 0, 1, // clang-format :-/
+	};
+
+	// 0 1-2 3
+	// 4 5-6 7
+	// 8 9-10 11
+
+	unsigned int ib[] = {
+	    0, 1, 4,
+	    4, 1, 5,
+	    4, 5, 8,
+	    8, 5, 9,
+	    2, 3, 6,
+	    6, 3, 7,
+	    6, 7, 10,
+	    10, 7, 11, // clang-format :-/
+	};
+
+	unsigned int res[24];
+	// with no locks, we should be able to collapse the entire mesh (vertices 1-2 and 9-10 are locked but others can move towards them)
+	assert(meshopt_simplifyWithAttributes(res, ib, 24, vb, 12, 12, NULL, 0, NULL, 0, NULL, 0, 1.f, 0) == 0);
+
+	// with corners locked, we should get two quads
+	assert(meshopt_simplifyWithAttributes(res, ib, 24, vb, 12, 12, NULL, 0, NULL, 0, lock0, 0, 1.f, 0) == 12);
+
+	// with both sides locked, we can only collapse the seam spine
+	assert(meshopt_simplifyWithAttributes(res, ib, 24, vb, 12, 12, NULL, 0, NULL, 0, lock1, 0, 1.f, 0) == 18);
+
+	// with seam spine locked, we can collapse nothing; note that we intentionally test two different lock configurations
+	// they each lock only one side of the seam spine, which should be equivalent
+	assert(meshopt_simplifyWithAttributes(res, ib, 24, vb, 12, 12, NULL, 0, NULL, 0, lock2, 0, 1.f, 0) == 24);
+	assert(meshopt_simplifyWithAttributes(res, ib, 24, vb, 12, 12, NULL, 0, NULL, 0, lock3, 0, 1.f, 0) == 24);
+}
+
 static void simplifySparse()
 {
 	float vb[] = {
@@ -1774,6 +1846,7 @@ void runTests()
 	simplifyAttr(/* skip_g= */ false);
 	simplifyAttr(/* skip_g= */ true);
 	simplifyLockFlags();
+	simplifyLockFlagsSeam();
 	simplifySparse();
 	simplifyErrorAbsolute();
 	simplifySeam();
diff --git a/src/simplifier.cpp b/src/simplifier.cpp
index 91be38b62..1fcf2f56b 100644
--- a/src/simplifier.cpp
+++ b/src/simplifier.cpp
@@ -369,12 +369,7 @@ static void classifyVertices(unsigned char* result, unsigned int* loop, unsigned
 	{
 		if (remap[i] == i)
 		{
-			if (vertex_lock && vertex_lock[sparse_remap ? sparse_remap[i] : i])
-			{
-				// vertex is explicitly locked
-				result[i] = Kind_Locked;
-			}
-			else if (wedge[i] == i)
+			if (wedge[i] == i)
 			{
 				// no attribute seam, need to check if it's manifold
 				unsigned int openi = openinc[i], openo = openout[i];
@@ -438,6 +433,18 @@ static void classifyVertices(unsigned char* result, unsigned int* loop, unsigned
 		}
 	}
 
+	if (vertex_lock)
+	{
+		// vertex_lock may lock any wedge, not just the primary vertex, so we need to lock the primary vertex and relock any wedges
+		for (size_t i = 0; i < vertex_count; ++i)
+			if (vertex_lock[sparse_remap ? sparse_remap[i] : i])
+				result[remap[i]] = Kind_Locked;
+
+		for (size_t i = 0; i < vertex_count; ++i)
+			if (result[remap[i]] == Kind_Locked)
+				result[i] = Kind_Locked;
+	}
+
 	if (options & meshopt_SimplifyLockBorder)
 		for (size_t i = 0; i < vertex_count; ++i)
 			if (result[i] == Kind_Border)