diff --git a/ci-nightly.sh b/ci-nightly.sh
index 46b19c5b7..bdb364f53 100755
--- a/ci-nightly.sh
+++ b/ci-nightly.sh
@@ -30,4 +30,3 @@ cargo batch  \
 
 cargo build --release --manifest-path embassy-executor/Cargo.toml --target avr-unknown-gnu-atmega328 -Z build-std=core,alloc --features nightly,arch-avr,avr-device/atmega328p
 cargo build --release --manifest-path embassy-executor/Cargo.toml --target avr-unknown-gnu-atmega328 -Z build-std=core,alloc --features nightly,arch-avr,integrated-timers,avr-device/atmega328p
-
diff --git a/ci.sh b/ci.sh
index ee2f320b5..36a6dea30 100755
--- a/ci.sh
+++ b/ci.sh
@@ -2,6 +2,12 @@
 
 set -eo pipefail
 
+# check-cfg is stable on rustc 1.79 but not cargo 1.79.
+# however, our cargo-batch is currently based on cargo 1.80, which does support check-cfg.
+# so, force build.rs scripts to emit check-cfg commands.
+# when 1.80 hits stable we can make build.rs unconditionally emit check-cfg and remove all this.
+export EMBASSY_FORCE_CHECK_CFG=1  
+
 export RUSTFLAGS=-Dwarnings
 export DEFMT_LOG=trace,embassy_hal_internal=debug,embassy_net_esp_hosted=debug,cyw43=info,cyw43_pio=info,smoltcp=info
 if [[ -z "${CARGO_TARGET_DIR}" ]]; then
diff --git a/embassy-executor/build_common.rs b/embassy-executor/build_common.rs
index 2c65f8529..0487eb3c5 100644
--- a/embassy-executor/build_common.rs
+++ b/embassy-executor/build_common.rs
@@ -70,6 +70,10 @@ impl CfgSet {
 }
 
 fn is_rustc_nightly() -> bool {
+    if env::var_os("EMBASSY_FORCE_CHECK_CFG").is_some() {
+        return true;
+    }
+
     let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
 
     let output = Command::new(rustc)
diff --git a/embassy-hal-internal/build_common.rs b/embassy-hal-internal/build_common.rs
index 2c65f8529..0487eb3c5 100644
--- a/embassy-hal-internal/build_common.rs
+++ b/embassy-hal-internal/build_common.rs
@@ -70,6 +70,10 @@ impl CfgSet {
 }
 
 fn is_rustc_nightly() -> bool {
+    if env::var_os("EMBASSY_FORCE_CHECK_CFG").is_some() {
+        return true;
+    }
+
     let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
 
     let output = Command::new(rustc)
diff --git a/embassy-stm32/build_common.rs b/embassy-stm32/build_common.rs
index 2c65f8529..0487eb3c5 100644
--- a/embassy-stm32/build_common.rs
+++ b/embassy-stm32/build_common.rs
@@ -70,6 +70,10 @@ impl CfgSet {
 }
 
 fn is_rustc_nightly() -> bool {
+    if env::var_os("EMBASSY_FORCE_CHECK_CFG").is_some() {
+        return true;
+    }
+
     let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
 
     let output = Command::new(rustc)
diff --git a/embassy-sync/build_common.rs b/embassy-sync/build_common.rs
index 2c65f8529..0487eb3c5 100644
--- a/embassy-sync/build_common.rs
+++ b/embassy-sync/build_common.rs
@@ -70,6 +70,10 @@ impl CfgSet {
 }
 
 fn is_rustc_nightly() -> bool {
+    if env::var_os("EMBASSY_FORCE_CHECK_CFG").is_some() {
+        return true;
+    }
+
     let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
 
     let output = Command::new(rustc)
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 57185e217..037fc5c6a 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,5 +1,5 @@
 [toolchain]
-channel = "1.78"
+channel = "1.79"
 components = [ "rust-src", "rustfmt", "llvm-tools" ]
 targets = [
     "thumbv7em-none-eabi",