diff --git a/ecp5/lpf.cc b/ecp5/lpf.cc
index e626cc54..e740b737 100644
--- a/ecp5/lpf.cc
+++ b/ecp5/lpf.cc
@@ -46,6 +46,9 @@ bool Arch::applyLPF(std::string filename, std::istream &in)
         while (std::getline(in, line)) {
             ++lineno;
             size_t cstart = line.find('#');
+            if (cstart != std::string::npos)
+                line = line.substr(0, cstart);
+            cstart = line.find("//");
             if (cstart != std::string::npos)
                 line = line.substr(0, cstart);
             if (isempty(line))