diff --git a/lib/std/priority_dequeue.zig b/lib/std/priority_dequeue.zig
index d154f5df5e..5bde0a36d0 100644
--- a/lib/std/priority_dequeue.zig
+++ b/lib/std/priority_dequeue.zig
@@ -43,13 +43,13 @@ pub fn PriorityDequeue(comptime T: type) type {
 
         /// Insert a new element, maintaining priority.
         pub fn add(self: *Self, elem: T) !void {
-            try ensureCapacity(self, self.len + 1);
+            try self.ensureUnusedCapacity(1);
             addUnchecked(self, elem);
         }
 
         /// Add each element in `items` to the dequeue.
         pub fn addSlice(self: *Self, items: []const T) !void {
-            try self.ensureCapacity(self.len + items.len);
+            try self.ensureUnusedCapacity(items.len);
             for (items) |e| {
                 self.addUnchecked(e);
             }
@@ -359,7 +359,11 @@ pub fn PriorityDequeue(comptime T: type) type {
             return queue;
         }
 
-        pub fn ensureCapacity(self: *Self, new_capacity: usize) !void {
+        /// Deprecated: call `ensureUnusedCapacity` or `ensureTotalCapacity`.
+        pub const ensureCapacity = ensureTotalCapacity;
+
+        /// Ensure that the dequeue can fit at least `new_capacity` items.
+        pub fn ensureTotalCapacity(self: *Self, new_capacity: usize) !void {
             var better_capacity = self.capacity();
             if (better_capacity >= new_capacity) return;
             while (true) {
@@ -369,6 +373,11 @@ pub fn PriorityDequeue(comptime T: type) type {
             self.items = try self.allocator.realloc(self.items, better_capacity);
         }
 
+        /// Ensure that the dequeue can fit at least `additional_count` **more** items.
+        pub fn ensureUnusedCapacity(self: *Self, additional_count: usize) !void {
+            return self.ensureTotalCapacity(self.len + additional_count);
+        }
+
         /// Reduce allocated capacity to `new_len`.
         pub fn shrinkAndFree(self: *Self, new_len: usize) void {
             assert(new_len <= self.items.len);
@@ -824,7 +833,7 @@ test "std.PriorityDequeue: shrinkAndFree" {
     var queue = PDQ.init(testing.allocator, lessThanComparison);
     defer queue.deinit();
 
-    try queue.ensureCapacity(4);
+    try queue.ensureTotalCapacity(4);
     try expect(queue.capacity() >= 4);
 
     try queue.add(1);
@@ -940,7 +949,7 @@ fn fuzzTestMinMax(rng: *std.rand.Random, queue_size: usize) !void {
 
 fn generateRandomSlice(allocator: *std.mem.Allocator, rng: *std.rand.Random, size: usize) ![]u32 {
     var array = std.ArrayList(u32).init(allocator);
-    try array.ensureCapacity(size);
+    try array.ensureTotalCapacity(size);
 
     var i: usize = 0;
     while (i < size) : (i += 1) {