diff --git a/coverage.jl b/coverage.jl
index d7c13633..7db2e34a 100644
--- a/coverage.jl
+++ b/coverage.jl
@@ -1,6 +1,7 @@
 using Coverage
 # process '*.cov' files
 coverage = process_folder() # defaults to src/; alternatively, supply the folder name as argument
+coverage = cat(coverage, process_folder("ext"); dims=1) # add coverage from ext/
 
 LCOV.writefile("lcov.info", coverage)
 
@@ -8,7 +9,7 @@ LCOV.writefile("lcov.info", coverage)
 coverage = merge_coverage_counts(
     coverage,
     filter!(
-        let prefixes = (joinpath(pwd(), "src", ""),)
+        let prefixes = (joinpath(pwd(), "src", ""), joinpath(pwd(), "ext", ""))
             c -> any(p -> startswith(c.filename, p), prefixes)
         end,
         LCOV.readfolder("test"),
diff --git a/ext/DynamicQuantitiesUnitfulExt.jl b/ext/DynamicQuantitiesUnitfulExt.jl
index c23902d8..4f79d258 100644
--- a/ext/DynamicQuantitiesUnitfulExt.jl
+++ b/ext/DynamicQuantitiesUnitfulExt.jl
@@ -34,6 +34,11 @@ Base.convert(::Type{DynamicQuantities.Quantity}, x::Unitful.Quantity) =
         return DynamicQuantities.Quantity(value, dimension)
     end
 
+Base.convert(::Type{DynamicQuantities.Quantity}, x::Unitful.FreeUnits) =
+    let
+        convert(DynamicQuantities.Quantity, 1.0 * x)
+    end
+
 Base.convert(::Type{DynamicQuantities.Dimensions}, d::Unitful.Dimensions{D}) where {D} =
     let
         cumulator = DynamicQuantities.Dimensions()
@@ -45,6 +50,11 @@ Base.convert(::Type{DynamicQuantities.Dimensions}, d::Unitful.Dimensions{D}) whe
         cumulator
     end
 
+Base.convert(::Type{DynamicQuantities.Dimensions}, x::Unitful.FreeUnits) =
+    let
+        DynamicQuantities.dimension(convert(DynamicQuantities.Quantity, x))
+    end
+
 function _map_dim_name_to_dynamic_units(::Type{Unitful.Dimension{D}}) where {D}
     # (We could do this automatically, but it's more obvious what we are doing this way.)
     D == :Length && return :length
@@ -54,7 +64,7 @@ function _map_dim_name_to_dynamic_units(::Type{Unitful.Dimension{D}}) where {D}
     D == :Temperature && return :temperature
     D == :Luminosity && return :luminosity
     D == :Amount && return :amount
-    error("Unknown dimension: $D")
+    throw(error("Unknown dimension: $D. Valid dimensions are: (:Length, :Mass, :Time, :Current, :Temperature, :Luminosity, :Amount)."))
 end
 
 
diff --git a/test/unitful.jl b/test/unitful.jl
index 243b1eca..860e0e72 100644
--- a/test/unitful.jl
+++ b/test/unitful.jl
@@ -8,3 +8,14 @@ x_unitful = 0.2u"mol^2*A^(-1//2)*cd^(2//5)"
 
 @test convert(Unitful.Quantity, x) ≈ x_unitful
 @test convert(DynamicQuantities.Quantity, convert(Unitful.Quantity, x)) ≈ x
+
+@test convert(DynamicQuantities.Quantity, u"c") ≈ 2.99792458e8 * DynamicQuantities.Dimensions(length=1, time=-1)
+@test convert(DynamicQuantities.Dimensions, u"c") == DynamicQuantities.Dimensions(length=1, time=-1)
+@test convert(DynamicQuantities.Dimensions, Unitful.dimension(u"c")) == DynamicQuantities.Dimensions(length=1, time=-1)
+
+# Defining a custom dimension should throw an error:
+Unitful.@dimension 𝚾 "𝚾" MyDimension
+# @refunit m "m" Meter 𝐋 true
+Unitful.@refunit my_unit "x" MyDimension 𝚾 true
+
+@test_throws "Unknown dimension: MyDimension" convert(DynamicQuantities.Quantity, 1.0 * my_unit)