diff --git a/source/coral/slab.zig b/source/coral/slab.zig
index 6d1957e..4dd6d30 100644
--- a/source/coral/slab.zig
+++ b/source/coral/slab.zig
@@ -52,17 +52,6 @@ pub fn Map(comptime index_int: std.builtin.Type.Int, comptime Value: type) type
 			entry.value = value;
 		}
 
-		///
-		/// Fetches the value referenced by `index` in `self`, returning it.
-		///
-		pub fn fetch(self: *Self, index: Index) Value {
-			const entry = &self.table[index];
-
-			debug.assert(entry.* == .value);
-
-			return entry.value;
-		}
-
 		///
 		/// Deinitializes `self` and sets it to an invalid state, freeing all memory allocated by `allocator`.
 		///
@@ -81,6 +70,17 @@ pub fn Map(comptime index_int: std.builtin.Type.Int, comptime Value: type) type
 			self.free_index = 0;
 		}
 
+		///
+		/// Fetches the value referenced by `index` in `self`, returning it.
+		///
+		pub fn fetch(self: *Self, index: Index) Value {
+			const entry = &self.table[index];
+
+			debug.assert(entry.* == .value);
+
+			return entry.value;
+		}
+
 		///
 		/// Attempts to grow the internal buffer of `self` by `growth_amount` using `allocator`.
 		///
@@ -147,12 +147,20 @@ pub fn Map(comptime index_int: std.builtin.Type.Int, comptime Value: type) type
 
 			debug.assert(entry.* == .free_index);
 
+			self.count += 1;
 			self.free_index = entry.free_index;
 			entry.* = .{.value = value};
 
 			return entry_index;
 		}
 
+		///
+		/// Returns `true` if `self` contains no values, otherwise `false`.
+		///
+		pub fn is_empty(self: Self) bool {
+			return self.count == 0;
+		}
+
 		///
 		/// Removes the value referenced by `index` from `self`.
 		///
@@ -161,6 +169,7 @@ pub fn Map(comptime index_int: std.builtin.Type.Int, comptime Value: type) type
 
 			debug.assert(entry.* == .value);
 
+			self.count -= 1;
 			entry.* = .{.free_index = self.free_index};
 			self.free_index = index;
 		}
diff --git a/source/ona/kym/Environment.zig b/source/ona/kym/Environment.zig
index 4969f3b..b23c243 100644
--- a/source/ona/kym/Environment.zig
+++ b/source/ona/kym/Environment.zig
@@ -183,6 +183,7 @@ pub fn deinit(self: *Self) void {
 	self.interned.deinit(self.allocator);
 	self.values.deinit(self.allocator);
 	self.calls.deinit(self.allocator);
+	coral.debug.assert(self.heap.is_empty());
 	self.heap.deinit(self.allocator);
 }