diff --git a/build/build-jasp.sh b/build/build-jasp.sh
index 6b47f92..1221525 100755
--- a/build/build-jasp.sh
+++ b/build/build-jasp.sh
@@ -520,6 +520,14 @@ staged_r="$STAGE_DIR$PREFIX/R/lib/R/lib"
 for lib in libR.so libRblas.so libRlapack.so; do
   [[ -f "$staged_r/$lib" ]] || { echo "error: staged tree lacks $lib" >&2; exit 1; }
 done
+# Without the bundled R's lib dir on the rpath, libR.so falls through to the
+# user's system R (Arch's `r` puts itself in ld.so.conf), whose libR lacks
+# internals like utf8clen: grDevices fails to load and so does every module.
+for bin in JASP JASPEngine; do
+  rp="$(patchelf --print-rpath "$STAGE_DIR$PREFIX/bin/$bin")"
+  [[ ":$rp:" == *":$PREFIX/R/lib/R/lib:"* ]] || {
+    echo "error: $bin rpath '$rp' lacks $PREFIX/R/lib/R/lib" >&2; exit 1; }
+done
 # Modules ship installed (module_libs/<module> over the binary_pkgs store), not
 # as .JASPModule bundles, so check that every module that built got installed.
 unstaged=()