diff --git a/.github/read_versions.sh b/.github/read_versions.sh
index 913c89e..d7e8b04 100644
--- a/.github/read_versions.sh
+++ b/.github/read_versions.sh
@@ -1,11 +1,15 @@
 # Sourced by CI jobs that need versions from nix/versions.nix.
 # Usage:  source .github/read_versions.sh
 # Exports: MOKU_VERSION  SUWA_VERSION  SUWA_HASH_LINUX  SUWA_HASH_MACOS_ARM64  SUWA_HASH_MACOS_X64  SUWA_HASH_WINDOWS
+#
+# Uses only POSIX -E grep (no -P) so this works on both GNU grep (Linux/Windows)
+# and BSD grep (macOS), which does not support -P/PCRE.
 
 _nix="$( cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd )/nix/versions.nix"
 _t=$(cat "$_nix")
 
-_pick() { echo "$_t" | grep -oP "${1}\s*=\s*\"\K[^\"]+"; }
+# Match `key = "value"` with -E, then strip the surrounding quotes.
+_pick() { echo "$_t" | grep -oE "${1}"'[[:space:]]*=[[:space:]]*"[^"]+"' | grep -oE '"[^"]+"' | tr -d '"'; }
 
 export MOKU_VERSION=$(_pick "moku")
 export SUWA_VERSION=$(_pick "version")