diff --git a/stm32/repro-build.sh b/stm32/repro-build.sh
index d5f62b56..89f51651 100644
--- a/stm32/repro-build.sh
+++ b/stm32/repro-build.sh
@@ -42,7 +42,7 @@ if [ -f *-v$VERSION_STRING-mk$MK_NUM-coldcard.dfu ]; then
     echo "Using existing binary in ../releases, not downloading."
 else
     # fetch a copy of the required binary
-    PUBLISHED_BIN=`grep v$VERSION_STRING-mk$MK_NUM-coldcard.dfu signatures.txt | dd bs=66 skip=1`
+    PUBLISHED_BIN=`grep -F v$VERSION_STRING-mk$MK_NUM-coldcard.dfu signatures.txt | dd bs=66 skip=1`
     if [ -z "$PUBLISHED_BIN" ]; then
         # may indicate first attempt to build this release
         echo "Cannot determine release date / full file name."