diff --git a/Project.toml b/Project.toml
index 61ad85e..eb41c5d 100644
--- a/Project.toml
+++ b/Project.toml
@@ -7,7 +7,6 @@ version = "0.11.2"
 BSplineKit = "093aae92-e908-43d7-9660-e50ee39d5a0a"
 DataDeps = "124859b0-ceae-595e-8997-d05f6a7a8dfe"
 FITSIO = "525bcba6-941b-5504-bd06-fd0dc1a4d2eb"
-Parameters = "d96e819e-fc66-5662-9728-84c9c7592b0a"
 Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
 UnitfulAstro = "6112ee07-acf9-5e0f-b108-d242c714bf9f"
 
@@ -15,7 +14,6 @@ UnitfulAstro = "6112ee07-acf9-5e0f-b108-d242c714bf9f"
 BSplineKit = "0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19"
 DataDeps = "0.7"
 FITSIO = "0.13.0, 0.14, 0.15, 0.16.1, 0.17"
-Parameters = "0.12"
 Unitful = "0.17.0, 1"
 UnitfulAstro = "0.3.0, 0.4, 1"
 julia = "1.6"
diff --git a/src/DustExtinction.jl b/src/DustExtinction.jl
index 1f2d116..01702c2 100644
--- a/src/DustExtinction.jl
+++ b/src/DustExtinction.jl
@@ -3,7 +3,6 @@ module DustExtinction
 import Unitful as U
 using UnitfulAstro: UnitfulAstro
 import DataDeps
-import Parameters
 import FITSIO as FITS
 import BSplineKit as BSK
 
@@ -40,8 +39,7 @@ The abstract supertype for dust extinction laws. See the extended help
 ## Interface
 
 Here's how to make a new extinction law, called `MyLaw`
-* Create your struct. We strongly recommend using `Parameters.jl` to facilitate
-  creating keyword argument constructors if your model is parameterized, which
+* Create your struct. We strongly recommend using keyword arguments if your model is parameterized, which
   allows convenient usage with [`redden`](@ref) and [`deredden`](@ref).
   ```julia
   struct MyLaw <: DustExtinction.ExtinctionLaw end
diff --git a/src/color_laws.jl b/src/color_laws.jl
index d7fcc83..e747583 100644
--- a/src/color_laws.jl
+++ b/src/color_laws.jl
@@ -18,7 +18,7 @@ for different coefficients used in the optical (3030.3 Å to 9090.9 Å).
 # See Also
 [`CCM89`](@ref)
 """
-Parameters.@with_kw struct OD94 <: ExtinctionLaw
+Base.@kwdef struct OD94 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
@@ -47,7 +47,7 @@ fit value for such galaxies was 4.05±0.80.
 # References
 [Calzetti et al. (2000)](https://ui.adsabs.harvard.edu/abs/2000ApJ...533..682C)
 """
-Parameters.@with_kw struct CAL00 <: ExtinctionLaw
+Base.@kwdef struct CAL00 <: ExtinctionLaw
     Rv::Float64 = 4.05
 end
 function (law::CAL00)(wave::T) where T
diff --git a/src/color_laws/ccm89.jl b/src/color_laws/ccm89.jl
index 0261d24..f8d67bb 100644
--- a/src/color_laws/ccm89.jl
+++ b/src/color_laws/ccm89.jl
@@ -18,7 +18,7 @@ A typical value for the Milky Way is 3.1.
 # References
 [Clayton,Cardelli and Mathis (1989)](https://ui.adsabs.harvard.edu/abs/1989ApJ...345..245C)
 """
-Parameters.@with_kw struct CCM89 <: ExtinctionLaw
+Base.@kwdef struct CCM89 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
diff --git a/src/color_laws/fitzpatrick.jl b/src/color_laws/fitzpatrick.jl
index 9ec9a72..2354adb 100644
--- a/src/color_laws/fitzpatrick.jl
+++ b/src/color_laws/fitzpatrick.jl
@@ -72,7 +72,7 @@ A typical value for the Milky Way is 3.1.
 # References
 [Fitzpatrick (1999)](https://ui.adsabs.harvard.edu/abs/1999PASP..111...63F/)
 """
-Parameters.@with_kw struct F99 <: ExtinctionLaw
+Base.@kwdef struct F99 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
@@ -165,7 +165,7 @@ See also Fitzpatrick & Massa (2007, ApJ, 663, 320)
 # References
 [Fitzpatrick (2004)](https://ui.adsabs.harvard.edu/abs/2004ASPC..309...33F/)
 """
-Parameters.@with_kw struct F04 <: ExtinctionLaw
+Base.@kwdef struct F04 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
@@ -242,7 +242,7 @@ sample of stars observed spectroscopically in the optical with HST/STIS.
 # References
 [Fitzpatrick (2019)](https://ui.adsabs.harvard.edu/abs/2019ApJ...886..108F/)
 """
-Parameters.@with_kw struct F19 <: ExtinctionLaw
+Base.@kwdef struct F19 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
diff --git a/src/color_laws/gcc09.jl b/src/color_laws/gcc09.jl
index 2a3bddf..f0677ec 100644
--- a/src/color_laws/gcc09.jl
+++ b/src/color_laws/gcc09.jl
@@ -9,7 +9,7 @@ This model was not derived for the optical or NIR.
 # References
 [Gordon, Cartledge, & Clayton (2009)](https://ui.adsabs.harvard.edu/abs/2009ApJ...705.1320G/)
 """
-Parameters.@with_kw struct GCC09 <: ExtinctionLaw
+Base.@kwdef struct GCC09 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
diff --git a/src/color_laws/m14.jl b/src/color_laws/m14.jl
index 019e474..b2e16be 100644
--- a/src/color_laws/m14.jl
+++ b/src/color_laws/m14.jl
@@ -65,7 +65,7 @@ equivalent to photometric R(V).
 # References
 [Maiz Apellaniz et al. (2014)](https://ui.adsabs.harvard.edu/abs/2014A%26A...564A..63M/)
 """
-Parameters.@with_kw struct M14 <: ExtinctionLaw
+Base.@kwdef struct M14 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
diff --git a/src/color_laws/vcg04.jl b/src/color_laws/vcg04.jl
index 55fc99f..c0f35c6 100644
--- a/src/color_laws/vcg04.jl
+++ b/src/color_laws/vcg04.jl
@@ -9,7 +9,7 @@ This model was not derived for the optical or NIR.
 # References
 [Valencic, Clayton, & Gordon (2004)](https://ui.adsabs.harvard.edu/abs/2004ApJ...616..912V/)
 """
-Parameters.@with_kw struct VCG04 <: ExtinctionLaw
+Base.@kwdef struct VCG04 <: ExtinctionLaw
     Rv::Float64 = 3.1
 end
 
diff --git a/src/fittable_laws.jl b/src/fittable_laws.jl
index 61b8f5b..e9e05d5 100644
--- a/src/fittable_laws.jl
+++ b/src/fittable_laws.jl
@@ -46,18 +46,20 @@ changing the expected behavior of reddening via the parameter ``A_V``.
 ## References
 [Fitzpatrick & Massa (1990)](https://ui.adsabs.harvard.edu/abs/1990ApJS...72..163F)
 """
-Parameters.@with_kw struct FM90{T<:Number} <: ExtinctionLaw @deftype T
-    c1 = 0.10
-    c2 = 0.70
-    c3 = 3.23
-    c4 = 0.41
-    x0 = 4.60
-    gamma = 0.99
-    @assert x0 ≥ 0 "`x0` must be ≥ 0, got $x0"
-    @assert gamma ≥ 0 "`gamma` must be ≥ 0, got $gamma"
+Base.@kwdef struct FM90{T<:Number} <: ExtinctionLaw
+    c1::T = 0.10
+    c2::T = 0.70
+    c3::T = 3.23
+    c4::T = 0.41
+    x0::T = 4.60
+    gamma::T = 0.99
+    function FM90(c1, c2, c3, c4, x0, gamma)
+        x0 < 0 && error("`x0` must be ≥ 0, got ", x0)
+        gamma < 0 && error("`gamma` must be ≥ 0, got ", gamma)
+        params = promote(c1, c2, c3, c4, x0, gamma)
+        return new{eltype(params)}(params...)
+    end
 end
-
-FM90(c1, c2, c3, c4, x0, gamma) = FM90(promote(c1, c2, c3, c4, x0, gamma)...)
 FM90(coeffs, x0=4.60, gamma=0.99) = FM90(coeffs..., x0, gamma)
 
 bounds(::Type{<:FM90}) = (912, 3200)
diff --git a/src/mixture_laws.jl b/src/mixture_laws.jl
index ec56d56..2d6f3d2 100644
--- a/src/mixture_laws.jl
+++ b/src/mixture_laws.jl
@@ -67,7 +67,7 @@ provide smooth interpolation as noted in Gordon et al. (2016, ApJ, 826, 104)
 # Reference
 [Gordon et al. (2003)](https://ui.adsabs.harvard.edu/abs/2003ApJ...594..279G/)
 """
-Parameters.@with_kw struct G03_SMCBar <: ExtinctionLaw
+Base.@kwdef struct G03_SMCBar <: DustExtinction.ExtinctionLaw
     Rv::Float64 = 2.74
     obsdata_x = g03_obsdata_x
     obsdata_axav = g03_obsdata_axav
@@ -82,7 +82,7 @@ Gordon et al. (2003) LMCAve Average Extinction Curve.
 # Reference
 [Gordon et al. (2003)](https://ui.adsabs.harvard.edu/abs/2003ApJ...594..279G/)
 """
-Parameters.@with_kw struct G03_LMCAve <: ExtinctionLaw
+Base.@kwdef struct G03_LMCAve <: DustExtinction.ExtinctionLaw
     Rv::Float64 = 3.41
     obsdata_x = g03lmc_obsdata_x
     obsdata_axav = g03lmc_obsdata_axav
@@ -170,9 +170,9 @@ A typical value for the Milky Way is 3.1.
 # References
 [Gordon et al. (2016)](https://ui.adsabs.harvard.edu/abs/2016ApJ...826..104G/)
 """
-Parameters.@with_kw struct G16{T<:Number} <: ExtinctionLaw @deftype T
+Base.@kwdef struct G16{T<:Number} <: ExtinctionLaw
     Rv::Float64 = 3.1
-    f_A = 1.0
+    f_A::T = 1.0
 end
 
 #G16(Rv, f_A) = G16(promote(Rv, f_A)...)
diff --git a/test/fittable_laws.jl b/test/fittable_laws.jl
index f3e6117..843b6f8 100644
--- a/test/fittable_laws.jl
+++ b/test/fittable_laws.jl
@@ -3,8 +3,11 @@
     x_inv_microns = [3.5, 4.0, 4.5, 5.0, 6.0, 7.0, 9.0, 10.0]
     wave = 1e4 ./ x_inv_microns
 
+    # Construction
     model = FM90()
     model1 = FM90([0.10 0.70 3.23 0.41])
+    @test_throws ErrorException("`x0` must be ≥ 0, got -2.0") FM90(x0=-2.0)
+    @test_throws ErrorException("`gamma` must be ≥ 0, got -2.0") FM90(gamma=-2.0)
 
     # Test out of bounds
     bad_waves = [100, 4e4]