diff --git a/passes/pmgen/ice40_dsp.pmg b/passes/pmgen/ice40_dsp.pmg
index 73e92031e..35db22807 100644
--- a/passes/pmgen/ice40_dsp.pmg
+++ b/passes/pmgen/ice40_dsp.pmg
@@ -189,6 +189,7 @@ match add
 	index <SigBit> port(add, AB)[0] === sigH[0]
 	filter GetSize(port(add, AB)) <= GetSize(sigH)
 	filter port(add, AB) ==  sigH.extract(0, GetSize(port(add, AB)))
+	filter nusers(sigH.extract_end(GetSize(port(add, AB)))) <= 1
 	set addAB AB
 	optional
 endmatch
diff --git a/passes/pmgen/xilinx_dsp.pmg b/passes/pmgen/xilinx_dsp.pmg
index f0537670f..20565f47d 100644
--- a/passes/pmgen/xilinx_dsp.pmg
+++ b/passes/pmgen/xilinx_dsp.pmg
@@ -268,6 +268,8 @@ match postAdd
 	select nusers(port(postAdd, AB)) <= 3
 	filter ffMcemux || nusers(port(postAdd, AB)) == 2
 	filter !ffMcemux || nusers(port(postAdd, AB)) == 3
+
+	index <SigBit> port(postAdd, AB)[0] === sigP[0]
 	filter GetSize(unextend(port(postAdd, AB))) <= GetSize(sigP)
 	filter unextend(port(postAdd, AB)) == sigP.extract(0, GetSize(unextend(port(postAdd, AB))))
 	filter nusers(sigP.extract_end(GetSize(unextend(port(postAdd, AB))))) <= 1