diff --git a/ci/run_task.sh b/ci/run_task.sh
index c05c157..f7b169e 100755
--- a/ci/run_task.sh
+++ b/ci/run_task.sh
@@ -30,7 +30,7 @@ usage() {
     cat <<EOF
 Usage:
 
-    ./run_task.sh TASK
+    ./run_task.sh TASK [CRATE1] [CRATE2] ...
 
 TASK
   - stable          Run tests with stable toolchain.
@@ -41,6 +41,11 @@ TASK
   - docsrs          Build docs with nightly toolchain.
   - bench           Run the bench tests.
 
+CRATES (optional)
+  - If provided, run the task only on the specified crate(s).
+  - Multiple crates can be specified as space-delimited arguments.
+  - If not provided, run the task on all crates from contrib/crates.sh.
+
 Environment Variables:
   MAINTAINER_TOOLS_LOG_LEVEL    Control script and cargo output verbosity.
     verbose (default)           Show all script and cargo messages.
@@ -52,11 +57,15 @@ main() {
     local task="${1:-usage}"
     local crates_script="$REPO_DIR/contrib/crates.sh"
 
-    # FIXME: This is a hackish way to get the help flag.
-    if [ "$task" = "usage" ] || [ "$task" = "-h" ] || [ "$task" = "--help" ]; then
-        usage
-        exit 0
-    fi
+    # Check for help flags in any position.
+    for arg in "$@"; do
+        case "$arg" in
+            -h|--help|help|usage)
+                usage
+                exit 0
+                ;;
+        esac
+    done
 
     check_required_commands
 
@@ -70,9 +79,16 @@ main() {
     fi
 
     verbose_say "Repository: $REPO_DIR"
-    verbose_say "Script invocation: $0 $task"
+    verbose_say "Script invocation: $0 $*"
 
-    if [ -e "$crates_script" ]; then
+    # Shift to remove the task argument, leaving only crate arguments.
+    shift
+
+    # Override crates.sh if there are crate args.
+    if [ "$#" -gt 0 ]; then
+        CRATES="$*"
+        verbose_say "Using specified crate(s): $CRATES"
+    elif [ -e "$crates_script" ]; then
         verbose_say "Sourcing $crates_script"
         # can't find the file because of the ENV var
         # shellcheck source=/dev/null
@@ -88,15 +104,15 @@ main() {
     stable)
         # Test, run examples, do feature matrix.
         # crate/contrib/test_vars.sh is sourced in this function.
-        build_and_test
+        build_and_test "stable"
         ;;
 
     nightly)
-        build_and_test
+        build_and_test "nightly"
         ;;
 
     msrv)
-        build_and_test
+        build_and_test "msrv"
         ;;
 
     lint)
@@ -124,7 +140,11 @@ main() {
 }
 
 # Build and test for each crate, done with each toolchain.
+#
+# Usage: build_and_test "toolchain"
 build_and_test() {
+    local toolchain="$1"
+
     for crate in $CRATES; do
         local test_vars_script="$REPO_DIR/$crate/contrib/test_vars.sh"
 
@@ -152,6 +172,7 @@ build_and_test() {
         fi
         pushd "$REPO_DIR/$crate" > /dev/null
 
+        need_toolchain "$toolchain"
         do_test
         do_feature_matrix
 
@@ -243,14 +264,14 @@ loop_features() {
 
 # Lint the workspace.
 do_lint_workspace() {
-    need_nightly
+    need_toolchain "nightly"
     $cargo clippy --workspace --all-targets --all-features --keep-going -- -D warnings
     $cargo clippy --workspace --all-targets --keep-going -- -D warnings
 }
 
 # Run extra crate specific lints, e.g. clippy with no-default-features.
 do_lint_crates() {
-    need_nightly
+    need_toolchain "nightly"
     for crate in $CRATES; do
         pushd "$REPO_DIR/$crate" > /dev/null
         if [ -e ./contrib/extra_lints.sh ]; then
@@ -307,7 +328,7 @@ do_dup_deps() {
 # Build the docs with a nightly toolchain, in unison with the function
 # below this checks that we feature guarded docs imports correctly.
 build_docs_with_nightly_toolchain() {
-    need_nightly
+    need_toolchain "nightly"
     # -j1 is because docs build fails if multiple versions of `bitcoin_hashes` are present in dep tree.
     RUSTDOCFLAGS="--cfg docsrs -D warnings -D rustdoc::broken-intra-doc-links" $cargo doc --all-features -j1
 }
@@ -315,12 +336,14 @@ build_docs_with_nightly_toolchain() {
 # Build the docs with a stable toolchain, in unison with the function
 # above this checks that we feature guarded docs imports correctly.
 build_docs_with_stable_toolchain() {
+    need_toolchain "stable"
     local cargo="cargo +stable --locked" # Can't use global because of `+stable`.
     RUSTDOCFLAGS="-D warnings" $cargo doc --all-features -j1
 }
 
 # Bench only works with a non-stable toolchain (nightly, beta).
 do_bench() {
+    need_toolchain "nightly"
     verbose_say "Running bench tests for: $CRATES"
 
     for crate in $CRATES; do
@@ -367,11 +390,44 @@ need_cmd() {
     fi
 }
 
-need_nightly() {
-    cargo_ver=$(cargo --version)
-    if echo "$cargo_ver" | grep -q -v nightly; then
-        err "Need a nightly compiler; have $(cargo --version)"
-    fi
+# Check that we have the required toolchain.
+need_toolchain() {
+    local required_toolchain="$1"
+    local current_toolchain
+    current_toolchain=$(rustc --version)
+
+    case "$required_toolchain" in
+        nightly)
+            if ! echo "$current_toolchain" | grep -q nightly; then
+                err "Need a nightly compiler; have $current_toolchain"
+            fi
+            ;;
+        stable)
+            if echo "$current_toolchain" | grep -q nightly || echo "$current_toolchain" | grep -q beta; then
+                err "Need a stable compiler; have $current_toolchain"
+            fi
+            ;;
+        msrv)
+            # This check must be run in a crate directory
+            # since it is possible for crates in a workspace to have different MSRVs.
+            local manifest_path
+            manifest_path="$(pwd)/Cargo.toml"
+            local msrv_version
+            msrv_version=$(cargo metadata --format-version 1 --no-deps | jq -r ".packages[] | select(.manifest_path == \"$manifest_path\") | .rust_version // empty")
+            if [ -z "$msrv_version" ]; then
+                err "No MSRV specified in $manifest_path or not in a crate directory"
+            fi
+
+            local current_version
+            current_version=$(echo "$current_toolchain" | grep -o '[0-9]\+\.[0-9]\+\.[0-9]\+' | head -1)
+            if [ "$current_version" != "$msrv_version" ]; then
+                err "Need Rust $msrv_version for MSRV testing in $manifest_path; have $current_version"
+            fi
+            ;;
+        *)
+            err "Unknown toolchain requirement: $required_toolchain"
+            ;;
+    esac
 }
 
 #
@@ -379,4 +435,3 @@ need_nightly() {
 #
 main "$@"
 exit 0
-