diff --git a/src/web/InputWaiter.mjs b/src/web/InputWaiter.mjs
index fec0f1b8..b59d1f86 100644
--- a/src/web/InputWaiter.mjs
+++ b/src/web/InputWaiter.mjs
@@ -1283,6 +1283,9 @@ class InputWaiter {
                 action: "updateTabHeader",
                 data: inputNum
             });
+        } else if (numTabs === this.maxTabs) {
+            // Can't create a new tab
+            document.getElementById("input-tabs").lastElementChild.style.boxShadow = "-15px 0px 15px -15px var(--primary-border-colour) inset";
         }
 
         if (changeTab) {
diff --git a/src/web/OutputWaiter.mjs b/src/web/OutputWaiter.mjs
index f6806ff3..2563d7e8 100755
--- a/src/web/OutputWaiter.mjs
+++ b/src/web/OutputWaiter.mjs
@@ -663,6 +663,9 @@ class OutputWaiter {
 
                 document.getElementById("save-all-to-file").style.display = "none";
             }
+        } else if (numTabs === this.maxTabs) {
+            // Can't create a new tab
+            document.getElementById("output-tabs").lastElementChild.style.boxShadow = "-15px 0px 15px -15px var(--primary-border-colour) inset";
         }
 
         if (changeTab) {