diff --git a/src/tools/compiletest/src/read2.rs b/src/tools/compiletest/src/read2.rs
index 4296dd3f5e00..68e9121250d4 100644
--- a/src/tools/compiletest/src/read2.rs
+++ b/src/tools/compiletest/src/read2.rs
@@ -9,7 +9,16 @@ use std::io::{self, Write};
 use std::mem::replace;
 use std::process::{Child, Output};
 
-pub fn read2_abbreviated(mut child: Child, filter_paths_from_len: &[String]) -> io::Result<Output> {
+#[derive(Copy, Clone, Debug)]
+pub enum Truncated {
+    Yes,
+    No,
+}
+
+pub fn read2_abbreviated(
+    mut child: Child,
+    filter_paths_from_len: &[String],
+) -> io::Result<(Output, Truncated)> {
     let mut stdout = ProcOutput::new();
     let mut stderr = ProcOutput::new();
 
@@ -24,7 +33,9 @@ pub fn read2_abbreviated(mut child: Child, filter_paths_from_len: &[String]) ->
     )?;
     let status = child.wait()?;
 
-    Ok(Output { status, stdout: stdout.into_bytes(), stderr: stderr.into_bytes() })
+    let truncated =
+        if stdout.truncated() || stderr.truncated() { Truncated::Yes } else { Truncated::No };
+    Ok((Output { status, stdout: stdout.into_bytes(), stderr: stderr.into_bytes() }, truncated))
 }
 
 const MAX_OUT_LEN: usize = 1024 * 1024;
@@ -46,6 +57,10 @@ impl ProcOutput {
         ProcOutput::Full { bytes: Vec::new(), filtered_len: 0 }
     }
 
+    fn truncated(&self) -> bool {
+        matches!(self, Self::Abbreviated { .. })
+    }
+
     fn extend(&mut self, data: &[u8], filter_paths_from_len: &[String]) {
         let new_self = match *self {
             ProcOutput::Full { ref mut bytes, ref mut filtered_len } => {
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 670441aacbd0..e2f29ca15872 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -12,7 +12,7 @@ use crate::compute_diff::{write_diff, write_filtered_diff};
 use crate::errors::{self, Error, ErrorKind};
 use crate::header::TestProps;
 use crate::json;
-use crate::read2::read2_abbreviated;
+use crate::read2::{read2_abbreviated, Truncated};
 use crate::util::{add_dylib_path, dylib_env_var, logv, PathBufExt};
 use crate::ColorConfig;
 use regex::{Captures, Regex};
@@ -701,6 +701,7 @@ impl<'test> TestCx<'test> {
             status: output.status,
             stdout: String::from_utf8(output.stdout).unwrap(),
             stderr: String::from_utf8(output.stderr).unwrap(),
+            truncated: Truncated::No,
             cmdline: format!("{cmd:?}"),
         };
         self.dump_output(&proc_res.stdout, &proc_res.stderr);
@@ -1275,6 +1276,7 @@ impl<'test> TestCx<'test> {
                 status,
                 stdout: String::from_utf8(stdout).unwrap(),
                 stderr: String::from_utf8(stderr).unwrap(),
+                truncated: Truncated::No,
                 cmdline,
             };
             if adb.kill().is_err() {
@@ -1557,7 +1559,13 @@ impl<'test> TestCx<'test> {
         };
 
         self.dump_output(&out, &err);
-        ProcRes { status, stdout: out, stderr: err, cmdline: format!("{:?}", cmd) }
+        ProcRes {
+            status,
+            stdout: out,
+            stderr: err,
+            truncated: Truncated::No,
+            cmdline: format!("{:?}", cmd),
+        }
     }
 
     fn cleanup_debug_info_options(&self, options: &Vec<String>) -> Vec<String> {
@@ -2218,7 +2226,7 @@ impl<'test> TestCx<'test> {
         dylib
     }
 
-    fn read2_abbreviated(&self, child: Child) -> Output {
+    fn read2_abbreviated(&self, child: Child) -> (Output, Truncated) {
         let mut filter_paths_from_len = Vec::new();
         let mut add_path = |path: &Path| {
             let path = path.display().to_string();
@@ -2265,12 +2273,13 @@ impl<'test> TestCx<'test> {
             child.stdin.as_mut().unwrap().write_all(input.as_bytes()).unwrap();
         }
 
-        let Output { status, stdout, stderr } = self.read2_abbreviated(child);
+        let (Output { status, stdout, stderr }, truncated) = self.read2_abbreviated(child);
 
         let result = ProcRes {
             status,
             stdout: String::from_utf8_lossy(&stdout).into_owned(),
             stderr: String::from_utf8_lossy(&stderr).into_owned(),
+            truncated,
             cmdline,
         };
 
@@ -3601,12 +3610,14 @@ impl<'test> TestCx<'test> {
             }
         }
 
-        let output = self.read2_abbreviated(cmd.spawn().expect("failed to spawn `make`"));
+        let (output, truncated) =
+            self.read2_abbreviated(cmd.spawn().expect("failed to spawn `make`"));
         if !output.status.success() {
             let res = ProcRes {
                 status: output.status,
                 stdout: String::from_utf8_lossy(&output.stdout).into_owned(),
                 stderr: String::from_utf8_lossy(&output.stderr).into_owned(),
+                truncated,
                 cmdline: format!("{:?}", cmd),
             };
             self.fatal_proc_rec("make failed", &res);
@@ -3768,6 +3779,12 @@ impl<'test> TestCx<'test> {
         let emit_metadata = self.should_emit_metadata(pm);
         let proc_res = self.compile_test(should_run, emit_metadata);
         self.check_if_test_should_compile(&proc_res, pm);
+        if matches!(proc_res.truncated, Truncated::Yes) {
+            self.fatal_proc_rec(
+                &format!("compiler output got truncated, cannot compare with reference file"),
+                &proc_res,
+            );
+        }
 
         // if the user specified a format in the ui test
         // print the output to the stderr file, otherwise extract
@@ -4459,6 +4476,7 @@ pub struct ProcRes {
     status: ExitStatus,
     stdout: String,
     stderr: String,
+    truncated: Truncated,
     cmdline: String,
 }