diff --git a/src/Unitful.jl b/src/Unitful.jl
index 9eb3339d..1a732189 100644
--- a/src/Unitful.jl
+++ b/src/Unitful.jl
@@ -787,7 +787,7 @@ isless(x::Number, y::Quantity) = _isless(promote(x,y)...)
 end
 
 isapprox{T,D,U}(x::Quantity{T,D,U}, y::Quantity{T,D,U}; atol=zero(Quantity{real(T),D,U}), kwargs...) =
-    isapprox(x.val, y.val; atol=atol.val, kwargs...)
+    isapprox(x.val, y.val; atol=uconvert(unit(y), atol).val, kwargs...)
 isapprox(x::Quantity, y::Quantity; kwargs...) = isapprox(uconvert(unit(y), x).val, y.val; kwargs...)
 isapprox(x::Quantity, y::Number; kwargs...) = isapprox(uconvert(NoUnits, x), y; kwargs...)
 isapprox(x::Number, y::Quantity; kwargs...) = isapprox(y,x; kwargs...)
diff --git a/test/runtests.jl b/test/runtests.jl
index 9bd03c64..9338e8ba 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -397,6 +397,8 @@ end
 
         @test isapprox(1.0u"m", 1.1u"m"; atol=0.2u"m")
         @test !isapprox(1.0u"m", 1.1u"m"; atol=0.05u"m")
+        @test isapprox(1.0u"m", 1.1u"m"; atol=200u"mm")
+        @test !isapprox(1.0u"m", 1.1u"m"; atol=50u"mm")
         @test isapprox(1.0u"m", 1.1u"m"; rtol=0.2)
         @test !isapprox(1.0u"m", 1.1u"m"; rtol=0.05)
     end