diff --git a/src/theoretical/variogram/circular.jl b/src/theoretical/variogram/circular.jl
index f7b6797..0e06cd8 100644
--- a/src/theoretical/variogram/circular.jl
+++ b/src/theoretical/variogram/circular.jl
@@ -9,6 +9,7 @@ struct CircularVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  CircularVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 CircularVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = CircularVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/cubic.jl b/src/theoretical/variogram/cubic.jl
index b664c98..ce8d25b 100644
--- a/src/theoretical/variogram/cubic.jl
+++ b/src/theoretical/variogram/cubic.jl
@@ -13,6 +13,7 @@ struct CubicVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  CubicVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 CubicVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = CubicVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/exponential.jl b/src/theoretical/variogram/exponential.jl
index aacc0de..135257d 100644
--- a/src/theoretical/variogram/exponential.jl
+++ b/src/theoretical/variogram/exponential.jl
@@ -13,6 +13,7 @@ struct ExponentialVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  ExponentialVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 ExponentialVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = ExponentialVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/gaussian.jl b/src/theoretical/variogram/gaussian.jl
index 63d8c13..179c99a 100644
--- a/src/theoretical/variogram/gaussian.jl
+++ b/src/theoretical/variogram/gaussian.jl
@@ -13,6 +13,7 @@ struct GaussianVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  GaussianVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 GaussianVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = GaussianVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/matern.jl b/src/theoretical/variogram/matern.jl
index 94de9f6..5e23bb9 100644
--- a/src/theoretical/variogram/matern.jl
+++ b/src/theoretical/variogram/matern.jl
@@ -15,6 +15,8 @@ struct MaternVariogram{V,O,B} <: Variogram
   nugget::V
   order::O
   ball::B
+  MaternVariogram(sill::V, nugget::V, order::O, ball::B) where {V,O,B} =
+    new{float(V),float(O),B}(sill, nugget, order, ball)
 end
 
 MaternVariogram(ball; sill=1.0, nugget=zero(typeof(sill)), order=1.0) = MaternVariogram(sill, nugget, order, ball)
diff --git a/src/theoretical/variogram/nugget.jl b/src/theoretical/variogram/nugget.jl
index 887b286..4b1b7e3 100644
--- a/src/theoretical/variogram/nugget.jl
+++ b/src/theoretical/variogram/nugget.jl
@@ -9,6 +9,7 @@ A pure nugget effect variogram with nugget `n`.
 """
 struct NuggetEffect{V} <: Variogram
   nugget::V
+  NuggetEffect(nugget::V) where {V} = new{float(V)}(nugget)
 end
 
 NuggetEffect(; nugget=1.0) = NuggetEffect(nugget)
diff --git a/src/theoretical/variogram/pentaspherical.jl b/src/theoretical/variogram/pentaspherical.jl
index 1e372dd..cf3af98 100644
--- a/src/theoretical/variogram/pentaspherical.jl
+++ b/src/theoretical/variogram/pentaspherical.jl
@@ -13,6 +13,7 @@ struct PentasphericalVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  PentasphericalVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 PentasphericalVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = PentasphericalVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/power.jl b/src/theoretical/variogram/power.jl
index afe8e2e..0c67956 100644
--- a/src/theoretical/variogram/power.jl
+++ b/src/theoretical/variogram/power.jl
@@ -11,6 +11,7 @@ struct PowerVariogram{V,E} <: Variogram
   scaling::V
   nugget::V
   exponent::E
+  PowerVariogram(scaling::V, nugget::V, exponent::E) where {V,E} = new{float(V),float(E)}(scaling, nugget, exponent)
 end
 
 PowerVariogram(; scaling=1.0, nugget=zero(typeof(scaling)), exponent=1.0) = PowerVariogram(scaling, nugget, exponent)
diff --git a/src/theoretical/variogram/sinehole.jl b/src/theoretical/variogram/sinehole.jl
index 5cf8ffe..2924892 100644
--- a/src/theoretical/variogram/sinehole.jl
+++ b/src/theoretical/variogram/sinehole.jl
@@ -13,6 +13,7 @@ struct SineHoleVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  SineHoleVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 SineHoleVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = SineHoleVariogram(sill, nugget, ball)
diff --git a/src/theoretical/variogram/spherical.jl b/src/theoretical/variogram/spherical.jl
index 3421089..5f1d7e0 100644
--- a/src/theoretical/variogram/spherical.jl
+++ b/src/theoretical/variogram/spherical.jl
@@ -13,6 +13,7 @@ struct SphericalVariogram{V,B} <: Variogram
   sill::V
   nugget::V
   ball::B
+  SphericalVariogram(sill::V, nugget::V, ball::B) where {V,B} = new{float(V),B}(sill, nugget, ball)
 end
 
 SphericalVariogram(ball; sill=1.0, nugget=zero(typeof(sill))) = SphericalVariogram(sill, nugget, ball)
diff --git a/test/theoretical/variogram.jl b/test/theoretical/variogram.jl
index cc2b030..6d9154c 100644
--- a/test/theoretical/variogram.jl
+++ b/test/theoretical/variogram.jl
@@ -189,6 +189,39 @@
   g = GeoStatsFunctions.scale(γ, 2)
   @test g == γ
 
+  # convert parameters to float
+  γ = CircularVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = CubicVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = ExponentialVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = GaussianVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = MaternVariogram(sill=1, nugget=1, order=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  @test γ.order isa Float64
+  γ = NuggetEffect(nugget=1)
+  @test nugget(γ) isa Float64
+  γ = PentasphericalVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = PowerVariogram(scaling=1, nugget=1, exponent=1)
+  @test γ.scaling isa Float64
+  @test nugget(γ) isa Float64
+  @test γ.exponent isa Float64
+  γ = SineHoleVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+  γ = SphericalVariogram(sill=1, nugget=1)
+  @test sill(γ) isa Float64
+  @test nugget(γ) isa Float64
+
   # shows
   γ = CircularVariogram()
   @test sprint(show, γ) == "CircularVariogram(sill: 1.0, nugget: 0.0, range: 1.0 m, distance: Euclidean)"