diff --git a/src/points.jl b/src/points.jl
index 67bc303..6e880d7 100644
--- a/src/points.jl
+++ b/src/points.jl
@@ -16,7 +16,7 @@ struct LLA{T <: Number}
     lon::T
     alt::T
 end
-LLA(lat, lon, alt=zero(lat)) = LLA(promote(lat, lon, alt)...)
+LLA(lat::Number, lon::Number, alt::Number=zero(lat)) = LLA(promote(lat, lon, alt)...)
 LLA(;lat=NaN,lon=NaN,alt=0.0) = LLA(lat,lon,alt) # Constructor that is idependent of storage order
 
 Base.show(io::IO, lla::LLA) = print(io, "LLA(lat=$(lla.lat)°, lon=$(lla.lon)°, alt=$(lla.alt))") # Maybe show to nearest mm, or 6 decimel places?
diff --git a/test/points.jl b/test/points.jl
index 7defa64..e9fd2c6 100644
--- a/test/points.jl
+++ b/test/points.jl
@@ -5,6 +5,7 @@
     @test LLA(lat = 1., lon = 1., alt = 0.) == lla
     @test LLA(1//1, 1, 0.) == lla
     @test LLA(1, 1) == LLA{Int}(1, 1, 0)
+    @test_throws MethodError LLA(missing, missing)
 
     latlon = LatLon(1., 1.)
     @test LatLon(lat = 1., lon = 1.) == latlon