diff --git a/ql-qlf-plugin/ql-dsp-io-regs.cc b/ql-qlf-plugin/ql-dsp-io-regs.cc
index 9f24594..7161203 100644
--- a/ql-qlf-plugin/ql-dsp-io-regs.cc
+++ b/ql-qlf-plugin/ql-dsp-io-regs.cc
@@ -66,7 +66,7 @@
             dsp->type = RTLIL::IdString(new_type);
 
             // Delete ports unused in given type of DSP cell
-            del_clk = (!reg_in_i && out_sel_i <= 3);
+            del_clk = (!reg_in_i && out_sel_i <= 3 && out_sel_i != 1);
 
             std::vector<std::string> ports2del;