diff --git a/docs/src/color_laws.md b/docs/src/color_laws.md
index 72232e0..6a78f2d 100644
--- a/docs/src/color_laws.md
+++ b/docs/src/color_laws.md
@@ -280,7 +280,9 @@ G16
 
 ```@docs
 redden
+redden!
 deredden
+deredden!
 DustExtinction.ExtinctionLaw
 DustExtinction.bounds
 DustExtinction.checkbounds
diff --git a/src/DustExtinction.jl b/src/DustExtinction.jl
index 52f3e22..84a55bb 100644
--- a/src/DustExtinction.jl
+++ b/src/DustExtinction.jl
@@ -7,7 +7,9 @@ import FITSIO as FITS
 import BSplineKit as BSK
 
 export redden,
+       redden!,
        deredden,
+       deredden!,
        # Rv laws
        CCM89,
        CAL00,
@@ -117,11 +119,23 @@ julia> redden(CCM89(Rv=3.1), wave, flux; Av=2)
 # See Also
 [`deredden`](@ref)
 """
-redden(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = redden(L(values(kwargs)...), wave, flux; Av = Av)
+redden(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = redden(L(values(kwargs)...), wave, flux; Av)
 redden(law::ExtinctionLaw, wave::Real, flux; Av = 1) = flux * 10^(-0.4 * Av * law(wave))
-redden(law::ExtinctionLaw, wave::U.Quantity, flux::Real; Av = 1) = redden(law, U.ustrip(U.u"Å", wave), flux; Av = Av)
+redden(law::ExtinctionLaw, wave::U.Quantity, flux::Real; Av = 1) = redden(law, U.ustrip(U.u"Å", wave), flux; Av)
 redden(law::ExtinctionLaw, wave::U.Quantity, flux::U.Quantity; Av = 1) = flux * (Av * law(wave))
 
+"""
+    redden!(::ExtinctionLaw, wave, flux; Av=1)
+    redden!(::Type{ExtinctionLaw}, wave, flux; Av=1, law_kwargs...)
+
+In-place version of [`redden`](@ref). Modifies `flux`.
+"""
+function redden!(law::ExtinctionLaw, wave, flux; Av = 1)
+    @. flux *= 10^(-0.4 * Av * law(wave))
+    return flux
+end
+redden!(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = redden!(L(values(kwargs)...), wave, flux; Av)
+
 """
     deredden(::ExtinctionLaw, wave, flux; Av=1)
     deredden(::Type{ExtinctionLaw}, wave, flux; Av=1, law_kwargs...)
@@ -148,11 +162,23 @@ julia> deredden(CCM89(Rv=3.1), wave, flux; Av=2)
 # See Also
 [`redden`](@ref)
 """
-deredden(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = deredden(L(values(kwargs)...), wave, flux; Av = Av)
+deredden(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = deredden(L(values(kwargs)...), wave, flux; Av)
 deredden(law::ExtinctionLaw, wave::Real, flux; Av = 1) = flux / 10^(-0.4 * Av * law(wave))
-deredden(law::ExtinctionLaw, wave::U.Quantity, flux::Real; Av = 1) = deredden(law, U.ustrip(U.u"Å", wave), flux; Av = Av)
+deredden(law::ExtinctionLaw, wave::U.Quantity, flux::Real; Av = 1) = deredden(law, U.ustrip(U.u"Å", wave), flux; Av)
 deredden(law::ExtinctionLaw, wave::U.Quantity, flux::U.Quantity; Av = 1) = flux / (Av * law(wave))
 
+"""
+    deredden!(::ExtinctionLaw, wave, flux; Av=1)
+    deredden!(::Type{ExtinctionLaw}, wave, flux; Av=1, law_kwargs...)
+
+In-place version of [`deredden`](@ref). Modifies `flux`.
+"""
+function deredden!(law::ExtinctionLaw, wave, flux; Av = 1)
+    @. flux /= 10^(-0.4 * Av * law(wave))
+    return flux
+end
+deredden!(L::Type{<:ExtinctionLaw}, wave, flux; Av = 1, kwargs...) = deredden!(L(values(kwargs)...), wave, flux; Av)
+
 # --------------------------------------------------------------------------------
 # bring in the support
 
diff --git a/test/runtests.jl b/test/runtests.jl
index 026f6ad..a40826a 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -54,9 +54,9 @@ using Test, Measurements, SkyCoords, Unitful, UnitfulAstro, Random
         ]
 
         flux = ones(length(wave))
-        output = @inferred broadcast((l, w, f)->redden(l, w, f; Av = 0.3), CCM89, wave, flux)
+        output = @inferred broadcast((l, w, f) -> redden(l, w, f; Av = 0.3), CCM89, wave, flux)
         @test output ≈ ref_values
-        @test @inferred(broadcast((l, w, f)->deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
+        @test @inferred(broadcast((l, w, f) -> deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
         flux .= redden.(CCM89, wave, flux, Av = 0.3)
         @test flux ≈ ref_values
 
@@ -67,21 +67,32 @@ using Test, Measurements, SkyCoords, Unitful, UnitfulAstro, Random
         @test redden.(CCM89, wave, flux) == redden.(CCM89(), wave, flux)
         @test redden.(CCM89, wave, flux, Rv = 2.8) == redden.(CCM89(Rv = 2.8), wave, flux)
 
+        # in-place reddening/de-reddening
+        flux_mut = copy(flux)
+        redden!(CCM89, wave, flux_mut)
+        @test redden.(CCM89, wave, flux) == flux_mut
+        flux_mut = copy(flux)
+        redden!(CCM89, wave, flux_mut, Rv = 2.8)
+        @test redden.(CCM89(Rv = 2.8), wave, flux) == flux_mut
+        flux_mut = copy(flux)
+        deredden!(CCM89, wave, flux_mut, Rv = 2.8)
+        @test flux_mut == deredden.(CCM89(Rv = 2.8), wave, flux)
+
         # Measurements
         flux = ones(length(wave)) .± 0.1
-        output = @inferred broadcast((l, w, f)->redden(l, w, f; Av = 0.3), CCM89, wave, flux)
+        output = @inferred broadcast((l, w, f) -> redden(l, w, f; Av = 0.3), CCM89, wave, flux)
         @test Measurements.value.(output) ≈ ref_values
-        @test @inferred(broadcast((l, w, f)->deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
+        @test @inferred(broadcast((l, w, f) -> deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
         flux .= redden.(CCM89, wave, flux, Av = 0.3)
         @test flux ≈ ref_values
 
         # Unitful
         flux = ones(length(wave))u"Jy"
         wave = wave * u"angstrom"
-        output = @inferred broadcast((l, w, f)->redden(l, w, f; Av = 0.3), CCM89, wave, flux)
+        output = @inferred broadcast((l, w, f) -> redden(l, w, f; Av = 0.3), CCM89, wave, flux)
         @test redden.(CCM89, wave, ustrip.(u"Jy", flux), Av = 0.3) ≈ ustrip.(u"Jy", output)
         @test ustrip.(output) ≈ ref_values
-        @test @inferred(broadcast((l, w, f)->deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
+        @test @inferred(broadcast((l, w, f) -> deredden(l, w, f; Av = 0.3), CCM89, wave, output)) ≈ flux
         @test deredden.(CCM89, wave, ustrip.(u"Jy", output), Av = 0.3) ≈ ustrip.(u"Jy", flux)
         flux .= redden.(CCM89, wave, flux, Av = 0.3)
         @test flux ≈ output