diff --git a/src/main.rs b/src/main.rs
index a6308a24e..6ff0c5df5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -224,6 +224,13 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         return Ok(());
     }
 
+    // A release build compiles the NES instruction trace out; say so before any trace line.
+    if let Some(warning) =
+        neser::platform::debugging::release_cpu_trace_warning(&args, cfg!(debug_assertions))
+    {
+        eprintln!("{warning}");
+    }
+
     // Initialize global tracing state (only active in debug builds)
     let tracing_config = app_context.borrow().config().frontend.tracing;
     neser::platform::debugging::init_tracing(tracing_config);
diff --git a/src/platform/config/cli.rs b/src/platform/config/cli.rs
index ed2beb32c..d5bab2a87 100644
--- a/src/platform/config/cli.rs
+++ b/src/platform/config/cli.rs
@@ -77,12 +77,12 @@ pub(crate) const PLATFORM_CLI_FLAGS: &[CliFlag] = &[
     },
     CliFlag {
         flag: "--trace",
-        help: Some("Enable CPU trace output"),
+        help: Some("Enable CPU trace output (instructions only in debug builds)"),
         has_value: false,
     },
     CliFlag {
         flag: "--trace-cpu",
-        help: Some("Enable CPU trace output"),
+        help: Some("Enable CPU trace output (instructions only in debug builds)"),
         has_value: false,
     },
     CliFlag {
@@ -868,6 +868,21 @@ mod tests {
         assert!(sound_section < sound_flag);
     }
 
+    #[test]
+    fn trace_flags_help_says_instructions_need_a_debug_build() {
+        let help = help_text();
+        for flag in ["--trace ", "--trace-cpu "] {
+            let line = help
+                .lines()
+                .find(|line| line.trim_start().starts_with(flag))
+                .unwrap_or_else(|| panic!("{flag} missing from help"));
+            assert!(
+                line.ends_with("Enable CPU trace output (instructions only in debug builds)"),
+                "{line}"
+            );
+        }
+    }
+
     #[test]
     fn test_help_text_lists_snes_filter_under_video_and_display() {
         assert_eq!(
diff --git a/src/platform/debugging/tracing.rs b/src/platform/debugging/tracing.rs
index aa1a8bdb4..b5ec99202 100644
--- a/src/platform/debugging/tracing.rs
+++ b/src/platform/debugging/tracing.rs
@@ -366,10 +366,102 @@ impl Tracing {
     }
 }
 
+/// The start-up warning for a CPU trace asked for on the command line of a build whose
+/// NES instruction trace is compiled out (a release build), or `None`.
+///
+/// Only the command line counts, so tracing enabled any other way never warns. The
+/// warning names the first CPU-trace spelling typed, without any `=N` level.
+pub fn release_cpu_trace_warning(args: &[String], debug_build: bool) -> Option<String> {
+    if debug_build {
+        return None;
+    }
+    let mut from_args = Tracing::default();
+    from_args.apply_args(args);
+    if from_args.cpu == 0 {
+        return None;
+    }
+    let flag = args.iter().find_map(|arg| match arg.as_str() {
+        "--trace" => Some("--trace"),
+        "--trace-cpu" => Some("--trace-cpu"),
+        other if other.starts_with("--trace-cpu=") => Some("--trace-cpu"),
+        _ => None,
+    })?;
+    Some(format!(
+        "warning: {flag}: this release build prints CPU interrupts only; build without --release for instruction lines"
+    ))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    fn args(list: &[&str]) -> Vec<String> {
+        std::iter::once("neser")
+            .chain(list.iter().copied())
+            .map(String::from)
+            .collect()
+    }
+
+    fn warning_for(flag: &str) -> String {
+        format!(
+            "warning: {flag}: this release build prints CPU interrupts only; build without --release for instruction lines"
+        )
+    }
+
+    #[test]
+    fn release_warning_names_trace_cpu() {
+        let warning = release_cpu_trace_warning(&args(&["--headless", "--trace-cpu"]), false);
+        assert_eq!(warning, Some(warning_for("--trace-cpu")));
+    }
+
+    #[test]
+    fn release_warning_names_trace() {
+        let warning = release_cpu_trace_warning(&args(&["--trace", "game.nes"]), false);
+        assert_eq!(warning, Some(warning_for("--trace")));
+    }
+
+    #[test]
+    fn release_warning_names_first_spelling_once() {
+        let warning = release_cpu_trace_warning(&args(&["--trace", "--trace-cpu"]), false);
+        assert_eq!(warning, Some(warning_for("--trace")));
+        let warning = release_cpu_trace_warning(&args(&["--trace-cpu", "--trace"]), false);
+        assert_eq!(warning, Some(warning_for("--trace-cpu")));
+        let warning = release_cpu_trace_warning(&args(&["--trace", "--trace"]), false).unwrap();
+        assert!(!warning.contains('\n'));
+    }
+
+    #[test]
+    fn release_warning_strips_level_value() {
+        let warning = release_cpu_trace_warning(&args(&["--trace-cpu=2"]), false);
+        assert_eq!(warning, Some(warning_for("--trace-cpu")));
+    }
+
+    #[test]
+    fn no_warning_in_debug_build() {
+        assert_eq!(release_cpu_trace_warning(&args(&["--trace"]), true), None);
+        assert_eq!(
+            release_cpu_trace_warning(&args(&["--trace-cpu"]), true),
+            None
+        );
+    }
+
+    #[test]
+    fn no_warning_without_cpu_trace_flag() {
+        assert_eq!(release_cpu_trace_warning(&args(&["game.nes"]), false), None);
+        let others = args(&["--trace-ppu", "--trace-nestest", "--gba-trace-cpu=1"]);
+        assert_eq!(release_cpu_trace_warning(&others, false), None);
+    }
+
+    #[test]
+    fn no_warning_when_cpu_level_is_zero() {
+        assert_eq!(
+            release_cpu_trace_warning(&args(&["--trace-cpu=0"]), false),
+            None
+        );
+        let off_again = args(&["--trace-cpu", "--trace-cpu=0"]);
+        assert_eq!(release_cpu_trace_warning(&off_again, false), None);
+    }
+
     fn parse_tracing(args: &[String]) -> Tracing {
         let mut tracing = Tracing::default();
         tracing.apply_args(args);