diff --git a/src/components/tabs/__snapshots__/tab.test.tsx.snap b/src/components/tabs/__snapshots__/tab.test.tsx.snap
index 72d29f99bdc..4e549710b56 100644
--- a/src/components/tabs/__snapshots__/tab.test.tsx.snap
+++ b/src/components/tabs/__snapshots__/tab.test.tsx.snap
@@ -13,7 +13,7 @@ exports[`EuiTab props append is rendered 1`] = `
     Append
   </span>
   <span
-    class="euiTab__content emotion-euiTab__content"
+    class="euiTab__content emotion-euiTab__content-m"
   >
     children
   </span>
@@ -29,7 +29,7 @@ exports[`EuiTab props disabled and selected 1`] = `
   type="button"
 >
   <span
-    class="euiTab__content emotion-euiTab__content-selected-disabled"
+    class="euiTab__content emotion-euiTab__content-m-selected-disabled"
   >
     Click Me
   </span>
@@ -45,7 +45,7 @@ exports[`EuiTab props disabled is rendered 1`] = `
   type="button"
 >
   <span
-    class="euiTab__content emotion-euiTab__content-disabled"
+    class="euiTab__content emotion-euiTab__content-m-disabled"
   >
     Click Me
   </span>
@@ -63,7 +63,7 @@ exports[`EuiTab props href renders anchor 1`] = `
   role="tab"
 >
   <span
-    class="euiTab__content emotion-euiTab__content"
+    class="euiTab__content emotion-euiTab__content-m"
   >
     children
   </span>
@@ -78,7 +78,7 @@ exports[`EuiTab props isSelected is rendered 1`] = `
   type="button"
 >
   <span
-    class="euiTab__content emotion-euiTab__content-selected"
+    class="euiTab__content emotion-euiTab__content-m-selected"
   >
     children
   </span>
@@ -95,7 +95,7 @@ exports[`EuiTab props onClick renders button 1`] = `
   type="button"
 >
   <span
-    class="euiTab__content emotion-euiTab__content"
+    class="euiTab__content emotion-euiTab__content-m"
   >
     children
   </span>
@@ -115,7 +115,7 @@ exports[`EuiTab props prepend is rendered 1`] = `
     Prepend
   </span>
   <span
-    class="euiTab__content emotion-euiTab__content"
+    class="euiTab__content emotion-euiTab__content-m"
   >
     children
   </span>
diff --git a/src/components/tabs/tab.tsx b/src/components/tabs/tab.tsx
index 3825375bbe2..c05b0d000c0 100644
--- a/src/components/tabs/tab.tsx
+++ b/src/components/tabs/tab.tsx
@@ -69,7 +69,7 @@ export const EuiTab: FunctionComponent<Props> = ({
   rel,
   prepend,
   append,
-  size,
+  size = 'm',
   expand,
   ...rest
 }) => {
diff --git a/upcoming_changelogs/6366.md b/upcoming_changelogs/6366.md
new file mode 100644
index 00000000000..92afa3a9b71
--- /dev/null
+++ b/upcoming_changelogs/6366.md
@@ -0,0 +1,3 @@
+**Bug fixes**
+
+- Fixed `EuiTab` not defaulting to size `m`