diff --git a/tamer/Makefile.am b/tamer/Makefile.am
index cefde6f8..e9e090c6 100644
--- a/tamer/Makefile.am
+++ b/tamer/Makefile.am
@@ -18,6 +18,13 @@
 #  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 ##
 
+# `Makefile.am` is processed by Automake into `Makefile.in`, which is then
+# processed by Autoconf into the final `Makefile`.
+#
+# The `@`-delimited variables are defined dynamically in `configure.ac`,
+# which is processed by Autoconf into `configure`; they are populated based
+# on the environment in which the `configure` script is invoked.
+
 .DELETE_ON_ERROR:
 
 .PHONY: all fix fmt check-fmt bench
@@ -30,27 +37,27 @@ all: bin doc
 
 .PHONY: bin
 bin:
-	@CARGO@ build $(CARGO_BUILD_FLAGS) @FEATURES@
+	@CARGO@ +@RUST_TC@ build $(CARGO_BUILD_FLAGS) @FEATURES@
 
 doc: html
 html-am:
-	@CARGO@ test --doc @FEATURES@
-	@CARGO@ @CARGO_DOC_FLAGS@ doc --document-private-items @FEATURES@
+	@CARGO@ +@RUST_TC@ test --doc @FEATURES@
+	@CARGO@ +@RUST_TC@ @CARGO_DOC_FLAGS@ doc --document-private-items @FEATURES@
 
 # note that 'cargo check' is something else; see 'cargo --help'
 test: check
 check-am: check-fmt
-	@CARGO@ test @FEATURES@
+	@CARGO@ +@RUST_TC@ test @FEATURES@
 
 check-fmt:
-	@CARGO@ fmt -- --check
+	@CARGO@ +@RUST_TC@ fmt -- --check
 
 bench:
-	@CARGO@ @CARGO_BENCH_PRE_FLAGS@ bench $(CARGO_BENCH_FLAGS) @FEATURES@
+	@CARGO@ +@RUST_TC@ @CARGO_BENCH_PRE_FLAGS@ bench $(CARGO_BENCH_FLAGS) @FEATURES@
 
 fix: fmt
 fmt:
-	@CARGO@ fmt
+	@CARGO@ +@RUST_TC@ fmt
 
 clean-am:
-	@CARGO@ clean
+	@CARGO@ +@RUST_TC@ clean
diff --git a/tamer/configure.ac b/tamer/configure.ac
index a506bb98..42d1db6f 100644
--- a/tamer/configure.ac
+++ b/tamer/configure.ac
@@ -43,13 +43,18 @@ AC_SUBST(SUFFIX, m4_argn(4, ver_split))
 AC_ARG_VAR([CARGO], [Rust Cargo executable])
 AC_CHECK_PROGS(CARGO, [cargo])
 
+# Rust toolchain (stable/nightly) is hard-coded for now, since decisions
+# regarding whether to use it are nuanced.
+AC_SUBST([RUST_TC], nightly)
+
 test -n "$CARGO" || AC_MSG_ERROR([cargo not found])
 
-rustc_ver_req=1.54.0
+# This is a nightly version at the time of writing
+rustc_ver_req=1.57.0
 
 AC_CHECK_PROGS(RUSTC, [rustc])
-AC_MSG_CHECKING([rustc version >= $rustc_ver_req])
-rustc_version=$("$RUSTC" --version | cut -d' ' -f2)
+AC_MSG_CHECKING([rustc $RUST_TC version >= $rustc_ver_req])
+rustc_version=$("$RUSTC" "+$RUST_TC" --version | cut -d' ' -f2)
 AX_COMPARE_VERSION([$rustc_version], [ge], [$rustc_ver_req],
                    [AC_MSG_RESULT([yes ($rustc_version)])],
                    [AC_MSG_RESULT([no ($rustc_version)])
@@ -66,30 +71,30 @@ AC_SUBST([CARGO_DOC_FLAGS], [])
 # it's still an unstable feature and we'll need to use nightly.  We don't
 # check for nightly here, though---if it's missing, then cargo will tell the
 # user what to do.
-AC_MSG_CHECKING([`test` feature support])
-AS_IF(["$RUSTC" --crate-type lib build_aux/bench_check.rs &>/dev/null],
+AC_MSG_CHECKING([`test` feature support on $RUST_TC])
+AS_IF(["$RUSTC" "+$RUST_TC" --crate-type lib build-aux/bench_check.rs &>/dev/null],
       [AC_MSG_RESULT(available)],
       [AC_MSG_RESULT([no (nightly required)])
        AC_SUBST([CARGO_BENCH_PRE_FLAGS], [+nightly])])
 
 # Cargo commands may be available but not necessarily installed for the
 # active toolchain.  Let's check that.
-AC_MSG_CHECKING([whether cargo-fmt is available for active toolchain])
-AS_IF([cargo fmt --help &>/dev/null],
+AC_MSG_CHECKING([whether cargo-fmt is available on $RUST_TC])
+AS_IF([cargo "+$RUST_TC" fmt --help &>/dev/null],
       [AC_MSG_RESULT(yes)],
       [AC_MSG_RESULT(no)
-       cargo fmt --help  # run again so user can see output
-       AC_MSG_ERROR([missing cargo-fmt for active toolchain])])
+       cargo "+$RUST_TC" fmt --help  # run again so user can see output
+       AC_MSG_ERROR([missing cargo-fmt on $RUST_TC])])
 
 # Cargo commands may be available but not necessarily installed for the
 # active toolchain.  Let's check that.
-AC_MSG_CHECKING([whether cargo-doc is available for toolchain])
-AS_IF([cargo $CARGO_DOC_FLAGS doc --help &>/dev/null],
+AC_MSG_CHECKING([whether cargo-doc is available on $RUST_TC])
+AS_IF([cargo "+$RUST_TC" $CARGO_DOC_FLAGS doc --help &>/dev/null],
       [AC_MSG_RESULT(yes)],
       [AC_MSG_RESULT(no)
        # run again so user can see output
-       cargo $CARGO_DOC_FLAGS doc --help 2>&1 | sed 's/^.*: //'
-       AC_MSG_WARN([missing cargo-doc for toolchain])
+       cargo "+$RUST_TC" $CARGO_DOC_FLAGS doc --help 2>&1 | sed 's/^.*: //'
+       AC_MSG_WARN([missing cargo-doc on $RUST_TC])
        AC_MSG_WARN([`make html` will not work])])
 
 AC_ARG_VAR([FEATURES],