diff --git a/README.md b/README.md
index ee8355c..02de5f7 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,16 @@ Here is a sample `hive.nix` with two nodes, with some common configurations appl
     environment.systemPackages = with pkgs; [
       vim wget curl
     ];
+
+    # By default, Colmena will replace unknown remote profile
+    # (unknown means the profile isn't in the nix store on the
+    # host running Colmena) during apply (with the default goal,
+    # boot, and switch).
+    # If you share a hive with others, or use multiple machines,
+    # and are not careful to always commit/push/pull changes
+    # you can accidentaly overwrite a remote profile so in those
+    # scenarios you might want to change this default to false. 
+    # deployment.replaceUnknownProfiles = true;
   };
 
   host-a = { name, nodes, ... }: {
@@ -87,6 +97,9 @@ Here is a sample `hive.nix` with two nodes, with some common configurations appl
     # environment variable to specify a ssh_config file.
     deployment.targetPort = 1234;
 
+    # Override the default for this target host
+    deployment.replaceUnknownProfiles = false;
+
     time.timeZone = "America/Los_Angeles";
 
     boot.loader.grub.device = "/dev/sda";
diff --git a/src/command/apply.rs b/src/command/apply.rs
index 5438326..30fdc06 100644
--- a/src/command/apply.rs
+++ b/src/command/apply.rs
@@ -91,6 +91,12 @@ To upload keys without building or deploying the rest of the configuration, use
             .help("Do not use gzip")
             .long_help("Disables the use of gzip when copying closures to the remote host.")
             .takes_value(false))
+        .arg(Arg::with_name("force-replace-unknown-profiles")
+            .long("force-replace-unknown-profiles")
+            .help("Ignore all targeted nodes deployment.replaceUnknownProfiles setting")
+            .long_help(r#"If `deployment.replaceUnknownProfiles` is set for a target, using this switch
+will treat deployment.replaceUnknownProfiles as though it was set true and perform unknown profile replacement."#)
+            .takes_value(false))
 }
 
 pub fn subcommand() -> App<'static, 'static> {
@@ -186,6 +192,7 @@ pub async fn run(_global_args: &ArgMatches<'_>, local_args: &ArgMatches<'_>) {
     options.set_gzip(!local_args.is_present("no-gzip"));
     options.set_progress_bar(!local_args.is_present("verbose"));
     options.set_upload_keys(!local_args.is_present("no-keys"));
+    options.set_force_replace_unknown_profiles(local_args.is_present("force-replace-unknown-profiles"));
 
     if local_args.is_present("keep-result") {
         options.set_gc_roots(hive_base.join(".gcroots"));
diff --git a/src/nix/deployment.rs b/src/nix/deployment.rs
index 6ac29c2..18ad1b0 100644
--- a/src/nix/deployment.rs
+++ b/src/nix/deployment.rs
@@ -10,10 +10,10 @@ use tokio::sync::{Mutex, Semaphore};
 use super::{Hive, Host, CopyOptions, NodeConfig, Profile, StoreDerivation, ProfileMap, host};
 use crate::progress::{Progress, TaskProgress, OutputStyle};
 
-/// Amount of RAM reserved for the system, in MB. 
+/// Amount of RAM reserved for the system, in MB.
 const EVAL_RESERVE_MB: u64 = 1024;
 
-/// Estimated amount of RAM needed to evaluate one host, in MB. 
+/// Estimated amount of RAM needed to evaluate one host, in MB.
 const EVAL_PER_HOST_MB: u64 = 512;
 
 const BATCH_OPERATION_LABEL: &'static str = "(...)";
@@ -493,6 +493,24 @@ impl Deployment {
 
         let mut bar = multi.create_task_progress(name.to_string());
 
+        // FIXME: Would be nicer to check remote status before spending time evaluating/building
+        if !target.config.replace_unknown_profiles {
+            bar.log("Checking remote profile...");
+            match target.host.active_derivation_known().await {
+                Ok(_) => {
+                    bar.log("Remote profile known");
+                }
+                Err(e) => {
+                    if self.options.force_replace_unknown_profiles {
+                        bar.log("warning: remote profile is unknown, but unknown profiles are being ignored");
+                    } else {
+                        bar.failure(&format!("Failed: {}", e));
+                        return;
+                    }
+                }
+            }
+        }
+
         if self.options.upload_keys && !target.config.keys.is_empty() {
             bar.log("Uploading keys...");
 
@@ -609,6 +627,9 @@ pub struct DeploymentOptions {
 
     /// Directory to create GC roots for node profiles in.
     gc_roots: Option<PathBuf>,
+
+    /// Ignore the node-level `deployment.replaceUnknownProfiles` option.
+    force_replace_unknown_profiles: bool,
 }
 
 impl Default for DeploymentOptions {
@@ -619,6 +640,7 @@ impl Default for DeploymentOptions {
             gzip: true,
             upload_keys: true,
             gc_roots: None,
+            force_replace_unknown_profiles: false,
         }
     }
 }
@@ -644,6 +666,10 @@ impl DeploymentOptions {
         self.gc_roots = Some(path.as_ref().to_owned());
     }
 
+    pub fn set_force_replace_unknown_profiles(&mut self, enable: bool) {
+        self.force_replace_unknown_profiles = enable;
+    }
+
     fn to_copy_options(&self) -> CopyOptions {
         let options = CopyOptions::default();
 
diff --git a/src/nix/eval.nix b/src/nix/eval.nix
index ffee416..cf04c0c 100644
--- a/src/nix/eval.nix
+++ b/src/nix/eval.nix
@@ -120,6 +120,22 @@ let
           type = types.attrsOf keyType;
           default = {};
         };
+        replaceUnknownProfiles = lib.mkOption {
+          description = ''
+            Allow a configuration to be applied to a host running a profile we
+            have no knowledge of. By setting this option to false, you reduce
+            the likelyhood of rolling back changes made via another Colmena user.
+
+            Unknown profiles are usually the result of either:
+            - The node had a profile applied, locally or by another Colmena.
+            - The host running Colmena garbage-collecting the profile.
+
+            To force profile replacement on all targeted nodes during apply,
+            use the flag `--force-replace-unknown-profiles`.
+          '';
+          type = types.bool;
+          default = true;
+        };
       };
     };
   };
diff --git a/src/nix/host/local.rs b/src/nix/host/local.rs
index 2a092b6..6d25e2e 100644
--- a/src/nix/host/local.rs
+++ b/src/nix/host/local.rs
@@ -92,6 +92,9 @@ impl Host for Local {
 
         result
     }
+    async fn active_derivation_known(&mut self) -> NixResult<bool> {
+        Ok(true)
+    }
     fn set_progress_bar(&mut self, bar: TaskProgress) {
         self.progress_bar = bar;
     }
diff --git a/src/nix/host/mod.rs b/src/nix/host/mod.rs
index c3e54ec..440b42d 100644
--- a/src/nix/host/mod.rs
+++ b/src/nix/host/mod.rs
@@ -102,7 +102,10 @@ pub trait Host: Send + Sync + std::fmt::Debug {
         Err(NixError::Unsupported)
     }
 
-    #[allow(unused_variables)] 
+    /// Check if the active profile is known to the host running Colmena
+    async fn active_derivation_known(&mut self) -> NixResult<bool>;
+
+    #[allow(unused_variables)]
     /// Activates a system profile on the host, if it runs NixOS.
     ///
     /// The profile must already exist on the host. You should probably use deploy instead.
diff --git a/src/nix/host/ssh.rs b/src/nix/host/ssh.rs
index 20316a5..6af34e9 100644
--- a/src/nix/host/ssh.rs
+++ b/src/nix/host/ssh.rs
@@ -7,7 +7,7 @@ use async_trait::async_trait;
 use tokio::process::Command;
 
 use super::{CopyDirection, CopyOptions, Host, key_uploader};
-use crate::nix::{StorePath, Profile, Goal, NixResult, NixCommand, Key, SYSTEM_PROFILE};
+use crate::nix::{StorePath, Profile, Goal, NixResult, NixCommand, NixError, Key, SYSTEM_PROFILE};
 use crate::util::CommandExecution;
 use crate::progress::TaskProgress;
 
@@ -70,6 +70,27 @@ impl Host for Ssh {
         let command = self.ssh(&v);
         self.run_command(command).await
     }
+    async fn active_derivation_known(&mut self) -> NixResult<bool> {
+        let paths = self.ssh(&["realpath", SYSTEM_PROFILE])
+            .capture_output()
+            .await;
+
+        match paths {
+            Ok(paths) => {
+                for path in paths.lines().into_iter() {
+                    let remote_profile: StorePath = path.to_string().try_into().unwrap();
+                    if remote_profile.exists() {
+                        return Ok(true);
+                    }
+                    return Err(NixError::ActiveProfileUnknown {
+                        store_path: path.to_string(),
+                    });
+                }
+                return Ok(false);
+            }
+            Err(e) => Err(e),
+        }
+    }
     fn set_progress_bar(&mut self, bar: TaskProgress) {
         self.progress_bar = bar;
     }
diff --git a/src/nix/mod.rs b/src/nix/mod.rs
index 25c2b65..4a1f88a 100644
--- a/src/nix/mod.rs
+++ b/src/nix/mod.rs
@@ -68,6 +68,9 @@ pub enum NixError {
     #[snafu(display("Invalid NixOS system profile"))]
     InvalidProfile,
 
+    #[snafu(display("Unknown active profile: {}", store_path))]
+    ActiveProfileUnknown { store_path: String },
+
     #[snafu(display("Nix Error: {}", message))]
     Unknown { message: String },
 }
@@ -105,6 +108,9 @@ pub struct NodeConfig {
     allow_local_deployment: bool,
     tags: Vec<String>,
 
+    #[serde(rename = "replaceUnknownProfiles")]
+    replace_unknown_profiles: bool,
+
     #[validate(custom = "validate_keys")]
     keys: HashMap<String, Key>,
 }