diff --git a/src/schema/resource.rs b/src/schema/resource.rs
index 3fac470..6957dda 100644
--- a/src/schema/resource.rs
+++ b/src/schema/resource.rs
@@ -45,6 +45,10 @@ impl Resource {
     }
 
     pub fn add_new_primary_subject(&mut self, mut subject: String) {
+        if subject == self.subject {
+            debug!("New and old subjects match, skipping...");
+            return;
+        }
         debug!("Swapping new and old subject");
         std::mem::swap(&mut subject, &mut self.subject);
         debug!("Pushing current subject into aliases");
@@ -95,6 +99,15 @@ pub mod test_data {
             links: None,
         }
     }
+
+    pub fn user_with_matching_subject_and_alias() -> Resource {
+        Resource {
+            subject: "acct:user@domain.tld".to_string(),
+            aliases: Some(vec!["acct:user@domain.tld".to_string()]),
+            properties: None,
+            links: None,
+        }
+    }
 }
 
 #[cfg(test)]
@@ -115,4 +128,45 @@ mod tests {
             }
         )
     }
+
+    #[test]
+    fn insert_new_primary_subject_into_new_user() {
+        let mut data = Resource::new("testing_subject".to_string());
+        data.add_new_primary_subject("new_subject".to_string());
+        assert_eq!(
+            data,
+            Resource {
+                subject: "new_subject".to_string(),
+                aliases: Some(vec!["testing_subject".to_string()]),
+                properties: None,
+                links: None
+            }
+        )
+    }
+
+    #[test]
+    fn insert_new_primary_subject_into_new_user_multiple_times() {
+        let mut data = Resource::new("testing_subject".to_string());
+        for _ in 0..10 {
+            data.add_new_primary_subject("new_subject".to_string())
+        }
+        assert_eq!(
+            data,
+            Resource {
+                subject: "new_subject".to_string(),
+                aliases: Some(vec!["testing_subject".to_string()]),
+                properties: None,
+                links: None
+            }
+        )
+    }
+
+    #[test]
+    fn check_preventing_alias_deduplication() {
+        let mut data = test_data::user_with_matching_subject_and_alias();
+        data.add_new_primary_subject("new_subject".to_string());
+        let mut check = test_data::user_with_matching_subject_and_alias();
+        check.subject = "new_subject".to_string();
+        assert_eq!(data, check)
+    }
 }