diff --git a/docs/src/circ_deque.md b/docs/src/circ_deque.md
index d39062a33..eb9697085 100644
--- a/docs/src/circ_deque.md
+++ b/docs/src/circ_deque.md
@@ -9,6 +9,7 @@ Usage:
 ```julia
 a = CircularDeque{Int}(n)   # allocate a deque with maximum capacity n
 isempty(a)          # test whether the deque is empty
+isfull(a)           # test whether the deque is full
 empty!(a)           # reset the deque
 capacity(a)         # return capacity
 length(a)           # get the number of elements currently in the deque
diff --git a/src/circ_deque.jl b/src/circ_deque.jl
index 3159d7d6a..4d7640415 100644
--- a/src/circ_deque.jl
+++ b/src/circ_deque.jl
@@ -23,6 +23,13 @@ Return the capacity of the circular deque
 """
 capacity(D::CircularDeque) = D.capacity
 
+"""
+    isfull(D::CircularDeque)
+
+Test whether the deque is full.
+"""
+isfull(D::CircularDeque) = length(D) == D.capacity
+
 function Base.empty!(D::CircularDeque)
     D.n = 0
     D.first = 1
diff --git a/test/test_circ_deque.jl b/test/test_circ_deque.jl
index adf3ddd6d..3ff729b10 100644
--- a/test/test_circ_deque.jl
+++ b/test/test_circ_deque.jl
@@ -64,6 +64,14 @@
             @test D[7-i] === 6
             @test popfirst!(D) === i
         end
+        empty!(D)
+        @test isfull(D) == false
+        for i = 1:4
+            push!(D, 1)
+        end
+        @test isfull(D) == false
+        push!(D, 1)
+        @test isfull(D) == true
     end
 
     @testset "pushfirst! works on an empty deque" begin