diff --git a/memoria/crates/memoria-api/tests/api_db_verify.rs b/memoria/crates/memoria-api/tests/api_db_verify.rs
index 4272aea6..97d3b6a5 100644
--- a/memoria/crates/memoria-api/tests/api_db_verify.rs
+++ b/memoria/crates/memoria-api/tests/api_db_verify.rs
@@ -531,6 +531,103 @@ async fn test_purge_by_topic_special_chars_verify_db() {
     println!("✅ purge by topic with special chars: LIKE fallback works");
 }
 
+#[tokio::test]
+#[serial]
+async fn test_purge_by_topic_treats_like_wildcards_literally_verify_db() {
+    let (base, client, server) = spawn_server().await;
+    let uid = uid();
+
+    // `_` and `%` in a topic are literal: purging "cfg_key" must not delete
+    // "cfgXkey", and "50%" must not delete "500 units".
+    for content in [
+        "rotate cfg_key monthly",
+        "rotate cfgXkey monthly",
+        "discount 50% applied",
+        "discount 500 units applied",
+    ] {
+        client
+            .post(format!("{base}/v1/memories"))
+            .header("X-User-Id", &uid)
+            .json(&json!({"content": content}))
+            .send()
+            .await
+            .unwrap();
+    }
+    assert_eq!(db_count_active(&server, &uid).await, 4);
+
+    for topic in ["cfg_key", "50%"] {
+        let r = client
+            .post(format!("{base}/v1/memories/purge"))
+            .header("X-User-Id", &uid)
+            .json(&json!({"topic": topic}))
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(r.status(), 200);
+        let body: Value = r.json().await.unwrap();
+        assert_eq!(body["purged"], 1, "topic {topic:?} must match literally");
+    }
+
+    assert_eq!(db_count_active(&server, &uid).await, 2);
+
+    // Topics that reach only the LIKE fallback (no literal match stored) must
+    // delete nothing: `_` is not a wildcard, and `'` / `\` are not replaced by
+    // spaces.
+    for (content, topic) in [
+        ("rotate cfgXkey monthly", "cfg_key"),
+        ("rotate ab cd daily", "ab'cd"),
+        ("rotate ab cd daily", "ab\\cd"),
+        ("rotate abXcd daily", "ab\\_cd"),
+    ] {
+        let user = crate::uid();
+        client
+            .post(format!("{base}/v1/memories"))
+            .header("X-User-Id", &user)
+            .json(&json!({"content": content}))
+            .send()
+            .await
+            .unwrap();
+        let r = client
+            .post(format!("{base}/v1/memories/purge"))
+            .header("X-User-Id", &user)
+            .json(&json!({"topic": topic}))
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(r.status(), 200);
+        let body: Value = r.json().await.unwrap();
+        assert_eq!(
+            body["purged"], 0,
+            "topic {topic:?} must not match {content:?}"
+        );
+        assert_eq!(db_count_active(&server, &user).await, 1);
+    }
+
+    // `'` and `\` themselves match literally.
+    for (content, topic) in [("note ab'cd here", "ab'cd"), ("path a\\b here", "a\\b")] {
+        let user = crate::uid();
+        client
+            .post(format!("{base}/v1/memories"))
+            .header("X-User-Id", &user)
+            .json(&json!({"content": content}))
+            .send()
+            .await
+            .unwrap();
+        let r = client
+            .post(format!("{base}/v1/memories/purge"))
+            .header("X-User-Id", &user)
+            .json(&json!({"topic": topic}))
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(r.status(), 200);
+        let body: Value = r.json().await.unwrap();
+        assert_eq!(body["purged"], 1, "topic {topic:?} must match {content:?}");
+        assert_eq!(db_count_active(&server, &user).await, 0);
+    }
+    println!("✅ purge by topic treats LIKE wildcards, quotes and backslashes literally");
+}
+
 #[tokio::test]
 #[serial]
 async fn test_purge_by_topic_batch_perf_verify_db() {
diff --git a/memoria/crates/memoria-storage/src/store.rs b/memoria/crates/memoria-storage/src/store.rs
index 147183be..82666569 100644
--- a/memoria/crates/memoria-storage/src/store.rs
+++ b/memoria/crates/memoria-storage/src/store.rs
@@ -842,16 +842,22 @@ pub fn validate_fulltext_query(query: &str) -> Result<(), MemoriaError> {
     Ok(())
 }
 
-/// Sanitize a string for use in a LIKE pattern (escapes `%`).
+/// Build the body of a `LIKE ?` pattern that matches `s` as a literal
+/// substring: `%`, `_` and the default escape character `\` are
+/// backslash-escaped so they cannot act as wildcards (a topic purge of `a_b`
+/// must not delete `aXb`). The default backslash escape is used instead of an
+/// `ESCAPE` clause because MatrixOne 4.1.x ignores custom `ESCAPE` characters.
+/// The pattern is a bind parameter, so `'` needs no special handling; only NUL
+/// is dropped.
 fn sanitize_like_pattern(s: &str) -> String {
-    s.chars()
-        .filter(|c| *c != '\0')
-        .map(|c| match c {
-            '\'' | '\\' => ' ',
-            '%' => ' ',
-            _ => c,
-        })
-        .collect()
+    let mut out = String::with_capacity(s.len());
+    for c in s.chars().filter(|c| *c != '\0') {
+        if matches!(c, '\\' | '%' | '_') {
+            out.push('\\');
+        }
+        out.push(c);
+    }
+    out
 }
 
 fn vec_to_mo(v: &[f32]) -> String {
@@ -6683,6 +6689,14 @@ mod tests {
     use std::io::{self, Write};
     use std::sync::{Arc, Mutex, OnceLock};
 
+    #[test]
+    fn sanitize_like_pattern_escapes_wildcards_for_literal_topic_match() {
+        assert_eq!(super::sanitize_like_pattern("user_id"), r"user\_id");
+        assert_eq!(super::sanitize_like_pattern("50% off!"), r"50\% off!");
+        assert_eq!(super::sanitize_like_pattern("it's a\\b\0"), r"it's a\\b");
+        assert_eq!(super::sanitize_like_pattern("plain topic"), "plain topic");
+    }
+
     static LOG_TEST_LOCK: OnceLock<Mutex<()>> = OnceLock::new();
 
     #[test]