diff --git a/xtask/src/bin_version.rs b/xtask/src/bin_version.rs
index 8b31108a..2a179453 100644
--- a/xtask/src/bin_version.rs
+++ b/xtask/src/bin_version.rs
@@ -11,3 +11,4 @@ pub const TYPOS_CLI: CargoPackage = CargoPackage::new("typos-cli", "1.29.5").wit
 pub const DIPLOMAT_TOOL: CargoPackage = CargoPackage::new("diplomat-tool", "0.7.1");
 
 pub const WABT_VERSION: &str = "1.0.36";
+pub const NIGHTLY_TOOLCHAIN: &str = "nightly-2025-07-28";
diff --git a/xtask/src/cov.rs b/xtask/src/cov.rs
index 85ab8067..4c957d85 100644
--- a/xtask/src/cov.rs
+++ b/xtask/src/cov.rs
@@ -160,8 +160,12 @@ pub fn report_github(sh: &Shell, repo: &str, pr_id: u32) -> anyhow::Result<()> {
 pub fn grcov(sh: &Shell) -> anyhow::Result<()> {
     let _s = Section::new("COV-GRCOV");
 
-    cmd!(sh, "rustup install nightly --profile=minimal").run()?;
-    cmd!(sh, "rustup component add --toolchain nightly llvm-tools-preview").run()?;
+    cmd!(sh, "rustup install {NIGHTLY_TOOLCHAIN} --profile=minimal").run()?;
+    cmd!(
+        sh,
+        "rustup component add --toolchain {NIGHTLY_TOOLCHAIN} llvm-tools-preview"
+    )
+    .run()?;
     cmd!(sh, "rustup component add llvm-tools-preview").run()?;
 
     cargo_install(sh, &CARGO_FUZZ)?;
@@ -181,7 +185,7 @@ pub fn grcov(sh: &Shell) -> anyhow::Result<()> {
         cmd!(sh, "{CARGO} clean").run()?;
 
         for target in FUZZ_TARGETS {
-            cmd!(sh, "rustup run nightly cargo fuzz coverage {target}").run()?;
+            cmd!(sh, "rustup run {NIGHTLY_TOOLCHAIN} cargo fuzz coverage {target}").run()?;
         }
 
         cmd!(sh, "cp -r ./target ../coverage/binaries/").run()?;
@@ -192,7 +196,7 @@ pub fn grcov(sh: &Shell) -> anyhow::Result<()> {
 
         cmd!(sh, "{CARGO} clean").run()?;
 
-        cmd!(sh, "rustup run nightly cargo test --workspace")
+        cmd!(sh, "rustup run {NIGHTLY_TOOLCHAIN} cargo test --workspace")
             .env("CARGO_INCREMENTAL", "0")
             .env("RUSTFLAGS", "-C instrument-coverage")
             .env("LLVM_PROFILE_FILE", "./coverage/default-%m-%p.profraw")
diff --git a/xtask/src/fuzz.rs b/xtask/src/fuzz.rs
index 29a731c5..08acf60b 100644
--- a/xtask/src/fuzz.rs
+++ b/xtask/src/fuzz.rs
@@ -17,9 +17,7 @@ pub fn corpus_minify(sh: &Shell, target: Option<String>) -> anyhow::Result<()> {
     };
 
     for target in targets {
-        cmd!(sh, "rustup run nightly cargo fuzz cmin {target}")
-            .env("RUSTUP_TOOLCHAIN", "nightly")
-            .run()?;
+        cmd!(sh, "rustup run {NIGHTLY_TOOLCHAIN} cargo fuzz cmin {target}").run()?;
     }
 
     Ok(())
@@ -63,7 +61,7 @@ pub fn install(sh: &Shell) -> anyhow::Result<()> {
 
     cargo_install(sh, &CARGO_FUZZ)?;
 
-    cmd!(sh, "rustup install nightly --profile=minimal").run()?;
+    cmd!(sh, "rustup install {NIGHTLY_TOOLCHAIN} --profile=minimal").run()?;
 
     Ok(())
 }
@@ -86,9 +84,8 @@ pub fn run(sh: &Shell, duration: Option<u32>, target: Option<String>) -> anyhow:
     for target in targets {
         cmd!(
             sh,
-            "rustup run nightly cargo fuzz run {target} -- -max_total_time={duration}"
+            "rustup run {NIGHTLY_TOOLCHAIN} cargo fuzz run {target} -- -max_total_time={duration}"
         )
-        .env("RUSTUP_TOOLCHAIN", "nightly")
         .run()?;
     }