diff --git a/src/backup.rs b/src/backup.rs
index 11153f7..0fa974e 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -11,8 +11,11 @@ pub struct Engine<'a> {
 }
 
 impl<'a> Engine<'a> {
-    pub fn new(source_path: &'a Path, repository: &'a mut Repository<'a>) -> Self {
-        Engine { source_path, repository }
+    pub fn new(source_path: &'a Path, repository: &'a mut Repository<'a>) -> Result<Self, BakareError> {
+        if source_path.ancestors().any(|a| a == repository.path()) {
+            return Err(BakareError::SourceSameAsRepository);
+        }
+        Ok(Engine { source_path, repository })
     }
 
     pub fn backup(&mut self) -> Result<(), BakareError> {
diff --git a/src/repository.rs b/src/repository.rs
index 9a884c6..a9f8963 100644
--- a/src/repository.rs
+++ b/src/repository.rs
@@ -76,6 +76,10 @@ impl<'a> Repository<'a> {
         }
     }
 
+    pub fn path(&self) -> &Path {
+        &self.path
+    }
+
     pub fn store(&mut self, source_path: &Path) -> Result<(), BakareError> {
         if !source_path.is_absolute() {
             return Err(BakareError::PathToStoreNotAbsolute);
diff --git a/src/test/assertions.rs b/src/test/assertions.rs
index 1160ddb..21536d8 100644
--- a/src/test/assertions.rs
+++ b/src/test/assertions.rs
@@ -6,10 +6,10 @@ use std::path::Path;
 use tempfile::tempdir;
 use walkdir::WalkDir;
 
-use crate::{backup, restore};
 use crate::error::BakareError;
 use crate::repository::{ItemVersion, Repository};
 use crate::source::TempSource;
+use crate::{backup, restore};
 
 pub fn assert_target_file_contents(restored_path: &Path, expected_contents: &str) -> Result<(), BakareError> {
     let mut actual_contents = String::new();
@@ -29,7 +29,7 @@ pub fn assert_same_after_restore(source_path: &Path) -> Result<(), BakareError>
     Repository::init(repository_path.as_path())?;
     {
         let mut backup_repository = Repository::open(repository_path.as_path())?;
-        let mut backup_engine = backup::Engine::new(source_path, &mut backup_repository);
+        let mut backup_engine = backup::Engine::new(source_path, &mut backup_repository)?;
         backup_engine.backup()?;
     }
     {
@@ -96,7 +96,7 @@ pub fn backup_file_with_contents(
 ) -> Result<(), BakareError> {
     {
         let mut backup_repository = Repository::open(repository_path)?;
-        let mut backup_engine = backup::Engine::new(source.path(), &mut backup_repository);
+        let mut backup_engine = backup::Engine::new(source.path(), &mut backup_repository)?;
         source.write_text_to_file(source_file_relative_path, contents)?;
         backup_engine.backup()?;
         Ok(())
diff --git a/tests/system_tests.rs b/tests/system_tests.rs
index 91b884e..e586150 100644
--- a/tests/system_tests.rs
+++ b/tests/system_tests.rs
@@ -1,5 +1,6 @@
 use tempfile::tempdir;
 
+use bakare::backup;
 use bakare::error::BakareError;
 use bakare::repository::Repository;
 use bakare::source::TempSource;
@@ -56,6 +57,23 @@ fn restore_older_version_of_file() -> Result<(), BakareError> {
     assert_restored_from_version_has_contents(&repository_path, &source_file_full_path, old_contents, &old_version)
 }
 
+#[test]
+fn forbid_backup_of_paths_within_repository() -> Result<(), BakareError> {
+    let repository_path = &tempdir()?.into_path();
+    Repository::init(repository_path)?;
+    let mut repository = Repository::open(repository_path)?;
+    if let Err(e) = backup::Engine::new(repository_path, &mut repository) {
+        let correct_error = match e {
+            BakareError::SourceSameAsRepository => true,
+            _ => false,
+        };
+        assert!(correct_error);
+    } else {
+        panic!("Expected error");
+    }
+    Ok(())
+}
+
 // TODO: restore latest version by default
 // TODO: deduplicate data
 // TODO: test that index is stored separately from data