diff --git a/asset/css/search-base.less b/asset/css/search-base.less
index 60253f49..d6f0e3b6 100644
--- a/asset/css/search-base.less
+++ b/asset/css/search-base.less
@@ -25,7 +25,8 @@
 
 .search-bar,
 .term-input-area {
-  [data-index] input:invalid {
+  [data-index] input:invalid,
+  [data-index] input.invalid {
     background-color: var(--search-term-invalid-bg, @search-term-invalid-bg);
     color: var(--search-term-invalid-color, @search-term-invalid-color);
   }
@@ -41,6 +42,23 @@
   }
 }
 
+.invalid-reason {
+  padding: .25em;
+  .rounded-corners(.25em);
+  border: 1px solid black;
+  font-weight: bold;
+  background: var(--search-term-invalid-reason-bg, @search-term-invalid-reason-bg);
+
+  opacity: 0;
+  visibility: hidden;
+  transition: opacity 2s, visibility 2s;
+  &.visible {
+    opacity: 1;
+    visibility: visible;
+    transition: none;
+  }
+}
+
 .search-suggestions {
   background: var(--suggestions-bg, @suggestions-bg);
   color: var(--suggestions-color, @suggestions-color);
@@ -236,6 +254,12 @@
           display: revert;
         }
       }
+
+      .invalid-reason {
+        position: absolute;
+        top: 85%;
+        left: .5em;
+      }
     }
   }
 }
diff --git a/asset/css/variables.less b/asset/css/variables.less
index a500c5e9..d1328fe6 100644
--- a/asset/css/variables.less
+++ b/asset/css/variables.less
@@ -60,6 +60,7 @@
 @search-term-selected-bg: @base-disabled;
 @search-term-invalid-bg: @state-critical;
 @search-term-invalid-color: @default-text-color-inverted;
+@search-term-invalid-reason-bg: @base-gray-lighter;
 @search-term-disabled-bg: @base-disabled;
 @search-term-selected-color: @base-gray-light;
 @search-term-highlighted-bg: @base-primary-bg;
@@ -154,6 +155,7 @@
     --search-term-selected-bg: var(--base-disabled);
     --search-term-invalid-bg: var(--base-remove-bg);
     --search-term-invalid-color: var(--default-text-color-inverted);
+    --search-term-invalid-reason-bg: var(--base-gray-lighter);
     --search-term-disabled-bg: var(--base-gray-light);
     --search-term-selected-color: var(--base-gray);
     --search-term-highlighted-bg: var(--primary-button-bg);
diff --git a/asset/js/widget/TermInput.js b/asset/js/widget/TermInput.js
index 7e8e891e..d405ae77 100644
--- a/asset/js/widget/TermInput.js
+++ b/asset/js/widget/TermInput.js
@@ -32,6 +32,21 @@ define(["../notjQuery", "BaseInput"], function ($, BaseInput) {
             this.ignoreSpaceUntil = null;
         }
 
+        registerTerm(termData, termIndex = null) {
+            termIndex = super.registerTerm(termData, termIndex);
+
+            if (this.readOnly) {
+                const label = this.termContainer.querySelector(`[data-index="${ termIndex }"]`);
+                if (label) {
+                    // The label only exists in DOM at this time if it was transmitted
+                    // by the server. So it's safe to assume that it needs validation
+                    this.validate(label.firstChild);
+                }
+            }
+
+            return termIndex;
+        }
+
         readPartialTerm(input) {
             let value = super.readPartialTerm(input);
             if (value && this.ignoreSpaceUntil && value[0] === this.ignoreSpaceUntil) {
@@ -75,6 +90,33 @@ define(["../notjQuery", "BaseInput"], function ($, BaseInput) {
             return super.hasSyntaxError(input);
         }
 
+        checkValidity(input) {
+            if (! this.readOnly) {
+                return super.checkValidity(input);
+            }
+
+            // Readonly terms don't participate in constraint validation, so we have to do it ourselves
+            return ! (input.pattern && ! input.value.match(input.pattern));
+        }
+
+        reportValidity(element) {
+            if (! this.readOnly) {
+                return super.reportValidity(element);
+            }
+
+            // Once invalid, it stays invalid since it's readonly
+            element.classList.add('invalid');
+            if (element.dataset.invalidMsg) {
+                const reason = element.parentNode.querySelector(':scope > .invalid-reason');
+                if (! reason.matches('.visible')) {
+                    element.title = element.dataset.invalidMsg;
+                    reason.textContent = element.dataset.invalidMsg;
+                    reason.classList.add('visible');
+                    setTimeout(() => reason.classList.remove('visible'), 5000);
+                }
+            }
+        }
+
         termsToQueryString(terms) {
             let quoted = [];
             for (const termData of terms) {
@@ -101,6 +143,7 @@ define(["../notjQuery", "BaseInput"], function ($, BaseInput) {
             if (this.readOnly) {
                 label.firstChild.readOnly = true;
                 label.appendChild($.render('<i class="icon fa-trash fa"></i>'));
+                label.appendChild($.render('<span class="invalid-reason"></span>'));
             }
 
             return label;
diff --git a/src/FormElement/TermInput/TermContainer.php b/src/FormElement/TermInput/TermContainer.php
index 5d3643ab..6bcf4dbb 100644
--- a/src/FormElement/TermInput/TermContainer.php
+++ b/src/FormElement/TermInput/TermContainer.php
@@ -52,7 +52,10 @@ protected function assemble()
                 )
             );
             if ($this->input->getReadOnly()) {
-                $label->addHtml(new Icon('trash'));
+                $label->addHtml(
+                    new Icon('trash'),
+                    new HtmlElement('span', Attributes::create(['class' => 'invalid-reason']))
+                );
             }
 
             $this->addHtml($label);