diff --git a/bin/hyperion-web/src/handlers/hostings.rs b/bin/hyperion-web/src/handlers/hostings.rs
index c30f4cf6..ee5d5bc3 100644
--- a/bin/hyperion-web/src/handlers/hostings.rs
+++ b/bin/hyperion-web/src/handlers/hostings.rs
@@ -1802,6 +1802,8 @@ pub struct PhpMemAutoView {
     pub raised_from_mb: Option<i64>,
     /// Last out-of-memory fatal seen; 0 = none since it was turned on.
     pub last_oom_at: i64,
+    /// The operator's own limit — what the ceiling must be above.
+    pub floor_mb: i64,
 }
 
 impl PhpMemAutoView {
@@ -1814,18 +1816,25 @@ impl PhpMemAutoView {
                 .map(|(_, v)| v.as_str())
         };
         let st = get(phpmem::KV_STATE).and_then(phpmem::State::parse);
+        let raised_from_mb = st
+            .as_ref()
+            .map(|s| s.base_mb)
+            .filter(|&b| b > 0 && b < current_mb);
         PhpMemAutoView {
             enabled: get(phpmem::KV_ENABLED) == Some("on"),
             max_mb: get(phpmem::KV_MAX_MB)
                 .and_then(|v| v.trim().parse().ok())
                 .unwrap_or(phpmem::DEFAULT_MAX_MB),
-            raised_from_mb: st
-                .as_ref()
-                .map(|s| s.base_mb)
-                .filter(|&b| b > 0 && b < current_mb),
+            raised_from_mb,
             last_oom_at: st.map(|s| s.last_oom_at).unwrap_or(0),
+            floor_mb: raised_from_mb.unwrap_or(current_mb),
         }
     }
+
+    /// Switched on with a ceiling that leaves nothing to raise to.
+    pub fn no_room(&self) -> bool {
+        self.enabled && hyperion_types::phpmem::ceiling_leaves_no_room(self.max_mb, self.floor_mb)
+    }
 }
 
 /// Operator-tunable php.ini settings, applied via a per-hosting
@@ -5074,6 +5083,56 @@ pub async fn post_set_limits(
     };
     let mem_auto_on = form.mem_auto.trim() == "on";
     let target = node_target(&form.target_node);
+    let hosting_id = find_hosting_anywhere(&state, sel.clone())
+        .await?
+        .0
+        .id
+        .as_str()
+        .to_string();
+    if mem_auto_on {
+        // A ceiling at or under the operator's own value gives the
+        // automation nothing to raise to — every out-of-memory would end as
+        // a daily "stuck at the ceiling" alert. Refuse it before anything is
+        // written. The floor is decided the way set_limits will decide it,
+        // from what the OWNING node has stored.
+        use hyperion_types::phpmem;
+        let stored = fetch_limits(&state, target, sel.clone())
+            .await
+            .ok()
+            .map(|l| l.php_memory_mb);
+        let st = match crate::dispatcher::dispatch_to_node(
+            &state,
+            target,
+            Request::HostingKvList {
+                hosting_id: hosting_id.clone(),
+            },
+        )
+        .await
+        {
+            Ok(RpcResponse::HostingKvList(v)) => v
+                .into_iter()
+                .find(|(k, _)| k == phpmem::KV_STATE)
+                .and_then(|(_, v)| phpmem::State::parse(&v)),
+            _ => None,
+        };
+        let floor = phpmem::floor_after_save(form.php_memory_mb, stored, st.as_ref());
+        if phpmem::ceiling_leaves_no_room(mem_auto_max, floor) {
+            let msg = format!(
+                "Automatic ceiling ({mem_auto_max} MB) must be above the site's own PHP memory \
+                 ({floor} MB), or there is nothing to raise to."
+            );
+            return Ok(save_result(
+                &headers,
+                false,
+                &msg,
+                format!(
+                    "/hostings/{}?flash_error={}#limits",
+                    urlencoding(&form.selector),
+                    urlencoding(&msg)
+                ),
+            ));
+        }
+    }
     let resp = crate::dispatcher::dispatch_to_node(
         &state,
         target,
@@ -5088,10 +5147,6 @@ pub async fn post_set_limits(
         // hosting_kv, beside the state its tick keeps — the pool it rewrites
         // is there. Written after the limits, so a refused save above leaves
         // them as they were.
-        let hosting_id = match find_hosting_anywhere(&state, sel).await {
-            Ok((d, _)) => d.id.as_str().to_string(),
-            Err(e) => return Err(e),
-        };
         for (key, value) in [
             (
                 hyperion_types::phpmem::KV_ENABLED,
diff --git a/bin/hyperion-web/templates/hostings_detail.html b/bin/hyperion-web/templates/hostings_detail.html
index 1d9f87fd..90df121c 100644
--- a/bin/hyperion-web/templates/hostings_detail.html
+++ b/bin/hyperion-web/templates/hostings_detail.html
@@ -2771,16 +2771,52 @@ <h2>
     <div class="field-row">
       <div class="field">
         <label class="field-checkbox" style="margin-top:1.6rem">
-          <input type="checkbox" name="mem_auto" value="on"{% if mem_auto.enabled %} checked{% endif %}>
+          <input id="mem_auto" type="checkbox" name="mem_auto" value="on"{% if mem_auto.enabled %} checked{% endif %}>
           <span>Raise PHP memory automatically when the site runs out <span class="hint">— +128 MB per step, back down after 2 quiet weeks</span></span>
         </label>
       </div>
       <div class="field">
         <label for="mem_auto_max_mb">Automatic ceiling <span class="hint">MB</span></label>
         <input id="mem_auto_max_mb" name="mem_auto_max_mb" type="number" min="16" max="8192"
-               value="{{ mem_auto.max_mb }}">
+               value="{{ mem_auto.max_mb }}"
+               data-shown-mb="{{ limits.php_memory_mb }}"
+               data-floor-mb="{{ mem_auto.floor_mb }}">
       </div>
     </div>
+    {# Ceiling at or under the site's own value = nothing to raise to; the
+       save refuses it. Rendered for a stored bad pair, kept live by the
+       script below while the fields are edited. Floor mirrors set_limits:
+       the shown (possibly raised) value resubmitted keeps the old floor. #}
+    <p id="mem_auto_warn" class="note text-warn" style="margin:0 0 0.8rem"{% if !mem_auto.no_room() %} hidden{% endif %}>
+      The ceiling must be above the site's own PHP memory (<span data-floor>{{ mem_auto.floor_mb }}</span> MB) —
+      at or under it the automation has nothing to raise to and only sends a daily
+      "still runs out at its ceiling" alert.
+    </p>
+    <script>
+    (function () {
+      'use strict';
+      const on = document.getElementById('mem_auto');
+      const max = document.getElementById('mem_auto_max_mb');
+      const mem = document.getElementById('php_memory_mb');
+      const warn = document.getElementById('mem_auto_warn');
+      if (!on || !max || !mem || !warn) return;
+      function check() {
+        const typed = parseInt(mem.value, 10);
+        const floor = String(typed) === max.dataset.shownMb
+          ? parseInt(max.dataset.floorMb, 10)
+          : typed;
+        const ceiling = parseInt(max.value, 10);
+        const bad = on.checked && Number.isFinite(floor) && Number.isFinite(ceiling) && ceiling <= floor;
+        warn.querySelector('[data-floor]').textContent = Number.isFinite(floor) ? floor : '?';
+        warn.hidden = !bad;
+      }
+      [on, max, mem].forEach(function (el) {
+        el.addEventListener('input', check);
+        el.addEventListener('change', check);
+      });
+      check();
+    })();
+    </script>
     {% if mem_auto.enabled %}
     <p class="note" style="margin:0 0 0.8rem">
       {% if let Some(from) = mem_auto.raised_from_mb %}Raised automatically from your {{ from }} MB to {{ limits.php_memory_mb }} MB.{% else %}At your own value.{% endif %}
diff --git a/crates/hyperion-types/src/phpmem.rs b/crates/hyperion-types/src/phpmem.rs
index 1108e790..5bdfdfd9 100644
--- a/crates/hyperion-types/src/phpmem.rs
+++ b/crates/hyperion-types/src/phpmem.rs
@@ -180,6 +180,24 @@ pub fn decide(
     Step::Nothing
 }
 
+/// The operator's own `memory_limit` once a limits-card save lands — the
+/// value the automation steps back down to, so the one its ceiling must be
+/// above. Mirrors `set_limits`: a value different from the stored one becomes
+/// the new floor; resubmitting the stored (possibly raised) value keeps the
+/// floor already in `st`.
+pub fn floor_after_save(typed_mb: i64, stored_mb: Option<i64>, st: Option<&State>) -> i64 {
+    match (stored_mb, st) {
+        (Some(stored), Some(s)) if typed_mb == stored && s.base_mb > 0 => s.base_mb,
+        _ => typed_mb,
+    }
+}
+
+/// A ceiling at or under the floor leaves the automation nothing to raise
+/// to: every out-of-memory ends as a "stuck at the ceiling" alert.
+pub fn ceiling_leaves_no_room(ceiling_mb: i64, floor_mb: i64) -> bool {
+    ceiling_mb <= floor_mb
+}
+
 /// Per-worker memory the node can afford: three quarters of its RAM shared
 /// by every worker the pool may run at once.
 pub fn ram_cap_mb(mem_total_mb: i64, max_children: i64) -> Option<i64> {
@@ -359,4 +377,31 @@ mod tests {
         assert_eq!(State::parse(r#"{"base_mb":128}"#), Some(st(128)));
         assert_eq!(State::parse("garbage"), None);
     }
+
+    #[test]
+    fn floor_after_save_follows_set_limits() {
+        // Raised 512 → 640; the card resubmits 640 unchanged: floor stays 512.
+        assert_eq!(floor_after_save(640, Some(640), Some(&st(512))), 512);
+        // A new value typed by hand is the new floor.
+        assert_eq!(floor_after_save(1024, Some(640), Some(&st(512))), 1024);
+        // No state yet (never on) or no stored row: the typed value.
+        assert_eq!(floor_after_save(1024, Some(1024), None), 1024);
+        assert_eq!(floor_after_save(256, None, Some(&st(512))), 256);
+        assert_eq!(floor_after_save(256, Some(256), Some(&st(0))), 256);
+    }
+
+    #[test]
+    fn a_ceiling_at_or_under_the_floor_leaves_no_room() {
+        // The reported case: 1024 MB of its own, ceiling 512.
+        assert!(ceiling_leaves_no_room(512, 1024));
+        assert!(ceiling_leaves_no_room(1024, 1024));
+        assert!(!ceiling_leaves_no_room(1152, 1024));
+        // And decide() agrees: an OOM there only ever reports Capped.
+        let mut s = st(1024);
+        s.last_oom_at = 1_000_000;
+        assert!(matches!(
+            decide(1_000_000, 1024, 512, None, &s),
+            Step::Capped { .. }
+        ));
+    }
 }