diff --git a/cache/memory/memory.go b/cache/memory/memory.go
index c5e36c3..38600ce 100644
--- a/cache/memory/memory.go
+++ b/cache/memory/memory.go
@@ -158,7 +158,8 @@ func (c *Cache) Set(key string, value []byte, ttl time.Duration) {
 		c.evictToFreeMemory(memoryToFree)
 	} else if atomic.LoadInt64(&c.entryCount) >= c.maxCacheSize {
 		// Fall back to count-based eviction for backward compatibility
-		c.evictOldest(int(c.maxCacheSize / 10)) // Evict 10% of entries
+		// 10% of entries, at least one: max/10 is 0 for caps below 10.
+		c.evictOldest(int(max(1, c.maxCacheSize/10)))
 	}
 
 	// A non-positive TTL is clamped to defaultTTL so this backend expires
diff --git a/cache/memory/small_cap_test.go b/cache/memory/small_cap_test.go
new file mode 100644
index 0000000..1a8f210
--- /dev/null
+++ b/cache/memory/small_cap_test.go
@@ -0,0 +1,23 @@
+package libpack_cache_memory
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Pins theorems/Theorems/MemCacheCap.lean: every cap >= 1 bounds the entry count.
+func TestSet_SmallEntryCapIsEnforced(t *testing.T) {
+	for _, maxEntries := range []int64{1, 2, 5, 9, 10, 25} {
+		t.Run(fmt.Sprintf("cap_%d", maxEntries), func(t *testing.T) {
+			c := NewWithSize(time.Minute, DefaultMaxMemorySize, maxEntries)
+			defer c.Shutdown()
+			for i := 0; i < 100; i++ {
+				c.Set(fmt.Sprintf("k%d", i), []byte("v"), time.Minute)
+				assert.LessOrEqual(t, c.CountQueries(), maxEntries)
+			}
+		})
+	}
+}