diff --git a/assets/css/custom.css b/assets/css/custom.css
index 67f07b2..e9922c6 100644
--- a/assets/css/custom.css
+++ b/assets/css/custom.css
@@ -275,11 +275,14 @@ body:not(.home) .menu { display: none; }
     pointer-events: none;
   }
   .proj-peek.is-visible { opacity: 1; visibility: visible; }
+  /* same fixed shape as the portfolio-index preview (.tui__preview img above)
+     — a plan and a photo have wildly different natural ratios, so without
+     this the peek box would jump size on every hover */
   .proj-peek img {
     width: 100%;
+    aspect-ratio: 3 / 2;
+    object-fit: cover;
     height: auto;
-    max-height: 70vh;
-    object-fit: contain;
     display: block;
     margin: 0;
   }