diff --git a/src/CoolProp.jl b/src/CoolProp.jl
index 2418248..0d8d29b 100644
--- a/src/CoolProp.jl
+++ b/src/CoolProp.jl
@@ -90,6 +90,7 @@ const _ha_units = Dict(
     "Tdb" => Unitful.u"K",
     "Twb" => Unitful.u"K",
     "Tdp" => Unitful.u"K",
+    "D" => Unitful.u"K",
     "H" => Unitful.u"J/kg",
     "Hha" => Unitful.u"J/kg",
     "U" => Unitful.u"J/kg",
@@ -104,9 +105,9 @@ const _ha_units = Dict(
     "P_w" => Unitful.u"Pa",
     )
 
-function _get_unit(param::AbstractString)
+function _get_unit(param::AbstractString, is_ha::Bool)
     # First check if it's a humid air parameter
-    if haskey(_ha_units, param)
+    if is_ha && haskey(_ha_units, param)
         return _ha_units[param]
     end
     # Otherwise use the normal parameter info
@@ -135,9 +136,9 @@ end
 _si_value(unit, value) = Unitful.ustrip(Unitful.uconvert(unit, value))
 
 function PropsSI(output::AbstractString, name1::AbstractString, value1::Union{Unitful.Quantity,Real}, name2::AbstractString, value2::Union{Unitful.Quantity,Real}, fluid::AbstractString)
-    unit1 = _get_unit(name1)
-    unit2 = _get_unit(name2)
-    outunit = _get_unit(output)
+    unit1 = _get_unit(name1,false)
+    unit2 = _get_unit(name2,false)
+    outunit = _get_unit(output,false)
     return PropsSI(output, name1, _si_value(unit1,value1), name2, _si_value(unit2,value2), fluid)*outunit
 end
 
@@ -713,10 +714,10 @@ function HAPropsSI(output::AbstractString, name1::AbstractString, value1::Real,
 end
 
 function HAPropsSI(output::AbstractString, name1::AbstractString, value1::Union{Unitful.Quantity,Real}, name2::AbstractString, value2::Union{Unitful.Quantity,Real}, name3::AbstractString, value3::Union{Unitful.Quantity,Real})
-    unit1 = _get_unit(name1)
-    unit2 = _get_unit(name2)
-    unit3 = _get_unit(name3)
-    outunit = _get_unit(output)
+    unit1 = _get_unit(name1,true)
+    unit2 = _get_unit(name2,true)
+    unit3 = _get_unit(name3,true)
+    outunit = _get_unit(output,true)
     return HAPropsSI(output, name1, _si_value(unit1,value1), name2, _si_value(unit2,value2), name3, _si_value(unit3,value3))*outunit
 end
 
diff --git a/test/testunits.jl b/test/testunits.jl
index 1b9c347..df4a46d 100644
--- a/test/testunits.jl
+++ b/test/testunits.jl
@@ -9,11 +9,13 @@ let fluid="air"
 
   # Test that all parameters return a unit
   for param in split(get_global_param_string("parameter_list"),',')
-    @test CoolProp._get_unit(param) isa FreeUnits
+    @test CoolProp._get_unit(param,false) isa FreeUnits
   end
 end
 
 let p=1atm, Tdb = 20°C, φ = 0.6
   x = HAPropsSI("HumRat", "Tdb", Tdb, "RH", φ, "P", p) |> g/kg
   @test round(g/kg, x; digits=2) == 8.77g/kg
+  Tdp = HAPropsSI("D", "T", 300K, "P", 101325Pa, "W", 0.01)
+  @test round(K,Tdp) == 287K
 end
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