diff --git a/src/StepToGeom/StepToGeom_MakeBSplineCurve.pxx b/src/StepToGeom/StepToGeom_MakeBSplineCurve.pxx
index d7ecabf8fb..4ea9525c1d 100644
--- a/src/StepToGeom/StepToGeom_MakeBSplineCurve.pxx
+++ b/src/StepToGeom/StepToGeom_MakeBSplineCurve.pxx
@@ -126,9 +126,9 @@
   BSplineCurve_retour CC;
   if (SC->IsKind(STANDARD_TYPE(StepGeom_BSplineCurveWithKnotsAndRationalBSplineCurve))) {
     const Handle(TColStd_HArray1OfReal)& aWeight = BSCWR->WeightsData();
-    TColStd_Array1OfReal W(1,NbPoles);
-    for (i=1; i<=NbPoles; i++)
-      W.SetValue(i,aWeight->Value(i));
+    TColStd_Array1OfReal W(1, NbPoles - aSumMulDiff);
+    for (i= 1 + aFMulDiff; i<= NbPoles - aLMulDiff; i++)
+      W.SetValue(i - aFMulDiff,aWeight->Value(i));
     CC = new BSplineCurve_gen(Poles, W, Kn, Mult, Deg, shouldBePeriodic);
   }
   else
diff --git a/tests/bugs/step/bug30921 b/tests/bugs/step/bug30921
new file mode 100644
index 0000000000..d30313f989
--- /dev/null
+++ b/tests/bugs/step/bug30921
@@ -0,0 +1,31 @@
+puts "========"
+puts "OCC30921"
+puts "========"
+puts ""
+##########################################################################
+# STEPCAFControl_Reader incorrectly reads the specified stp file
+##########################################################################
+
+stepread [locate_data_file bug30921.stp] a *
+tpcompound result
+
+checkprops result -s 288180 
+puts "REQUIRED All: Faulty shapes in variables faulty_1 to faulty_39"
+checkshape result
+
+set nbshapes_expected "
+Number of shapes in shape
+ VERTEX    : 2858
+ EDGE      : 4331
+ WIRE      : 1758
+ FACE      : 1514
+ SHELL     : 21
+ SOLID     : 21
+ COMPSOLID : 0
+ COMPOUND  : 1
+ SHAPE     : 10504
+"
+
+
+checknbshapes result -ref ${nbshapes_expected} -t -m "Shape"
+checkview -display result -3d -path ${imagedir}/${test_image}.png