diff --git a/.changelog/_unreleased.toml b/.changelog/_unreleased.toml
new file mode 100644
index 00000000..a57b66fb
--- /dev/null
+++ b/.changelog/_unreleased.toml
@@ -0,0 +1,5 @@
+[[entries]]
+id = "67c15e74-a142-482f-9d2e-972a50161129"
+type = "feature"
+description = "Make Rust builds respect Cargo.lock when present"
+author = "jon.gjengset@helsing.ai"
diff --git a/kraken-build/src/kraken/std/cargo/manifest.py b/kraken-build/src/kraken/std/cargo/manifest.py
index c5d6536e..e1ad1879 100644
--- a/kraken-build/src/kraken/std/cargo/manifest.py
+++ b/kraken-build/src/kraken/std/cargo/manifest.py
@@ -70,7 +70,7 @@ class CargoMetadata:
     target_directory: Path
 
     @classmethod
-    def read(cls, project_dir: Path) -> CargoMetadata:
+    def read(cls, project_dir: Path, locked: bool | None = None) -> CargoMetadata:
         cmd = [
             "cargo",
             "metadata",
@@ -79,6 +79,16 @@ def read(cls, project_dir: Path) -> CargoMetadata:
             "--manifest-path",
             str(project_dir / "Cargo.toml"),
         ]
+        if locked is None:
+            project_dir = project_dir.absolute()
+            for parent in [project_dir, *project_dir.parents]:
+                if (parent / "Cargo.lock").exists():
+                    cmd.append("--locked")
+                    break
+        elif locked:
+            # if locked is True, we should *always* pass --locked.
+            # the expectation is that the command will fail w/o Cargo.lock.
+            cmd.append("--locked")
         result = subprocess.run(cmd, stdout=subprocess.PIPE)
         if result.returncode != 0:
             logger.error("Stderr: %s", result.stderr)
diff --git a/kraken-build/src/kraken/std/cargo/tasks/cargo_build_task.py b/kraken-build/src/kraken/std/cargo/tasks/cargo_build_task.py
index fac0d015..3d019031 100644
--- a/kraken-build/src/kraken/std/cargo/tasks/cargo_build_task.py
+++ b/kraken-build/src/kraken/std/cargo/tasks/cargo_build_task.py
@@ -5,6 +5,7 @@
 import subprocess as sp
 import time
 from dataclasses import dataclass
+from pathlib import Path
 
 from kraken.core import Project, Property, Task, TaskStatus
 from kraken.std.cargo.manifest import ArtifactKind, CargoMetadata
@@ -35,6 +36,11 @@ class CargoBuildTask(Task):
     #: Whether to build incrementally or not.
     incremental: Property[bool | None] = Property.default(None)
 
+    #: Whether to pass --locked to cargo or not.
+    #:
+    #: When set to None, --locked is passed if Cargo.lock exists.
+    locked: Property[bool | None] = Property.default(None)
+
     #: Environment variables for the Cargo command.
     env: Property[dict[str, str]] = Property.default_factory(dict)
 
@@ -58,11 +64,31 @@ def get_description(self) -> str | None:
     def get_cargo_command_additional_flags(self) -> list[str]:
         return shlex.split(os.environ.get("KRAKEN_CARGO_BUILD_FLAGS", ""))
 
+    def should_add_locked_flag(self) -> bool:
+        locked = self.locked.get()
+        if locked is None:
+            # pass --locked if we have a lock file
+            # since we may be in a workspace member, we need to search up!
+            for parent in (Path.cwd() / "Cargo.toml").parents:
+                if (parent / "Cargo.lock").exists():
+                    return True
+        elif locked:
+            # if locked is True, we should *always* pass --locked.
+            # the expectation is that the command will fail w/o Cargo.lock.
+            return True
+        return False
+
+    def get_additional_args(self) -> list[str]:
+        args = self.additional_args.get()
+        if "--locked" not in args and self.should_add_locked_flag():
+            args = ["--locked", *args]
+        return args
+
     def get_cargo_command(self, env: dict[str, str]) -> list[str]:
         incremental = self.incremental.get()
         if incremental is not None:
             env["CARGO_INCREMENTAL"] = "1" if incremental else "0"
-        return ["cargo", "build"] + self.additional_args.get()
+        return ["cargo", "build"] + self.get_additional_args()
 
     def make_safe(self, args: list[str], env: dict[str, str]) -> None:
         pass
diff --git a/kraken-build/src/kraken/std/cargo/tasks/cargo_publish_task.py b/kraken-build/src/kraken/std/cargo/tasks/cargo_publish_task.py
index be57ab8a..332c7c21 100644
--- a/kraken-build/src/kraken/std/cargo/tasks/cargo_publish_task.py
+++ b/kraken-build/src/kraken/std/cargo/tasks/cargo_publish_task.py
@@ -35,6 +35,7 @@ def get_cargo_command(self, env: dict[str, str]) -> list[str]:
             raise ValueError(f'registry {registry.alias!r} missing a "publish_token"')
         command = (
             ["cargo", "publish"]
+            + (["--locked"] if self.should_add_locked_flag() else [])
             + self.additional_args.get()
             + ["--registry", registry.alias, "--token", registry.publish_token]
             + ([] if self.verify.get() else ["--no-verify"])
diff --git a/kraken-build/src/kraken/std/cargo/tasks/cargo_test_task.py b/kraken-build/src/kraken/std/cargo/tasks/cargo_test_task.py
index 8d0c4a03..1ad8daf2 100644
--- a/kraken-build/src/kraken/std/cargo/tasks/cargo_test_task.py
+++ b/kraken-build/src/kraken/std/cargo/tasks/cargo_test_task.py
@@ -9,4 +9,4 @@ class CargoTestTask(CargoBuildTask):
 
     def get_cargo_command(self, env: dict[str, str]) -> list[str]:
         super().get_cargo_command(env)
-        return ["cargo", "test"] + self.additional_args.get()
+        return ["cargo", "test"] + self.get_additional_args()