diff --git a/dev/conbench_envs/hooks.sh b/dev/conbench_envs/hooks.sh
index 60a482adfcf..5cf75a5c734 100755
--- a/dev/conbench_envs/hooks.sh
+++ b/dev/conbench_envs/hooks.sh
@@ -59,6 +59,25 @@ build_arrow_python() {
 
 build_arrow_r() {
   cat ci/etc/rprofile >> $(R RHOME)/etc/Rprofile.site
+
+  # Ensure CXX20 is configured in R's Makeconf.
+  # conda-forge's R may have empty CXX20 entries even though the compiler supports it.
+  # Arrow requires C++20, so we need to add these settings if missing.
+  MAKECONF="$(R RHOME)/etc/Makeconf"
+  if [ -z "$(R CMD config CXX20)" ]; then
+    echo "*** CXX20 not configured in R, adding it to Makeconf"
+    cat >> "$MAKECONF" << 'EOF'
+
+# Added for Arrow C++20 support
+CXX20 = g++
+CXX20FLAGS = -g -O2 $(LTO)
+CXX20PICFLAGS = -fpic
+CXX20STD = -std=gnu++20
+SHLIB_CXX20LD = $(CXX20) $(CXX20STD)
+SHLIB_CXX20LDFLAGS = -shared
+EOF
+  fi
+
   ci/scripts/r_deps.sh $(pwd) $(pwd)
   (cd r; R CMD INSTALL .;)
 }