diff --git a/landing/src/app/ui/contact-form.scss b/landing/src/app/ui/contact-form.scss
index 67997d3..9a1edab 100644
--- a/landing/src/app/ui/contact-form.scss
+++ b/landing/src/app/ui/contact-form.scss
@@ -81,3 +81,42 @@
     --pi-theme-field-radius: 1.25rem;
   }
 }
+
+// Error states, which move the form around and read wrong.
+//
+// 1. Submitting an incomplete form shoved everything below it downwards.
+//    Material's subscript strip is 10px tall while a field is valid and 24px
+//    once it carries a message, so every errored field grew the form by 14px at
+//    once — the fields under the cursor jumped out from under it. Reserving the
+//    taller height up front costs 14px of whitespace and buys a form that does
+//    not move.
+//
+// 2. `pi-checkbox` renders its message as an inline span straight after the
+//    label, so it ran on as part of the sentence: "Acepto que guardéis mis
+//    datos para responderme. Hace falta tu consentimiento". It belongs on its
+//    own line, like every other field's message.
+:host ::ng-deep {
+  .pi-field .mat-mdc-form-field-subscript-wrapper {
+    min-height: 1.5rem;
+  }
+
+  // Its own line, in space reserved for it. Left in flow it would push the
+  // submit button 25px down at the exact moment you press it — the same jump
+  // the reserved subscript above removes for the fields.
+  .pi-checkbox {
+    position: relative;
+    padding-bottom: 1.25rem;
+  }
+
+  // Nothing in the library styles this class, so the message inherited the
+  // body colour and read as ordinary text next to four red ones.
+  .pi-checkbox__error {
+    display: block;
+    position: absolute;
+    left: 0;
+    bottom: 0;
+    color: var(--pi-color-warn);
+    // `mat-error` renders the other four at 12px; this one inherited 15px.
+    font-size: var(--pi-font-size-x-small, 0.75rem);
+  }
+}