diff --git a/src/implementations/BigFloat.jl b/src/implementations/BigFloat.jl
index f72ad5b0..2aa0929c 100644
--- a/src/implementations/BigFloat.jl
+++ b/src/implementations/BigFloat.jl
@@ -61,6 +61,10 @@ function operate_to!(output::BigFloat, ::typeof(+), a::BigFloat, b::BigFloat)
     return output
 end
 
+operate_to!(out::BigFloat, ::typeof(+), a::BigFloat) = operate_to!(out, copy, a)
+
+operate!(::typeof(+), a::BigFloat) = a
+
 # -
 
 promote_operation(::typeof(-), ::Vararg{Type{BigFloat},N}) where {N} = BigFloat
@@ -78,32 +82,36 @@ function operate_to!(output::BigFloat, ::typeof(-), a::BigFloat, b::BigFloat)
     return output
 end
 
-function operate!(::typeof(-), x::BigFloat)
+function operate_to!(o::BigFloat, ::typeof(-), x::BigFloat)
     ccall(
         (:mpfr_neg, :libmpfr),
         Int32,
         (Ref{BigFloat}, Ref{BigFloat}, Base.MPFR.MPFRRoundingMode),
-        x,
+        o,
         x,
         Base.MPFR.ROUNDING_MODE[],
     )
-    return x
+    return o
 end
 
+operate!(::typeof(-), x::BigFloat) = operate_to!(x, -, x)
+
 # Base.abs
 
-function operate!(::typeof(Base.abs), x::BigFloat)
+function operate_to!(o::BigFloat, ::typeof(Base.abs), x::BigFloat)
     ccall(
         (:mpfr_abs, :libmpfr),
         Int32,
         (Ref{BigFloat}, Ref{BigFloat}, Base.MPFR.MPFRRoundingMode),
-        x,
+        o,
         x,
         Base.MPFR.ROUNDING_MODE[],
     )
-    return x
+    return o
 end
 
+operate!(::typeof(Base.abs), x::BigFloat) = operate_to!(x, abs, x)
+
 # *
 
 promote_operation(::typeof(*), ::Type{BigFloat}, ::Type{BigFloat}) = BigFloat
@@ -121,6 +129,10 @@ function operate_to!(output::BigFloat, ::typeof(*), a::BigFloat, b::BigFloat)
     return output
 end
 
+operate_to!(out::BigFloat, ::typeof(*), a::BigFloat) = operate_to!(out, copy, a)
+
+operate!(::typeof(*), a::BigFloat) = a
+
 # Base.fma
 
 function promote_operation(
diff --git a/src/implementations/BigInt.jl b/src/implementations/BigInt.jl
index 36aa8c45..c6102115 100644
--- a/src/implementations/BigInt.jl
+++ b/src/implementations/BigInt.jl
@@ -33,6 +33,10 @@ function operate_to!(output::BigInt, ::typeof(+), a::BigInt, b::BigInt)
     return Base.GMP.MPZ.add!(output, a, b)
 end
 
+operate_to!(out::BigInt, ::typeof(+), a::BigInt) = operate_to!(out, copy, a)
+
+operate!(::typeof(+), a::BigInt) = a
+
 # -
 
 promote_operation(::typeof(-), ::Vararg{Type{BigInt},N}) where {N} = BigInt
@@ -41,6 +45,10 @@ function operate_to!(output::BigInt, ::typeof(-), a::BigInt, b::BigInt)
     return Base.GMP.MPZ.sub!(output, a, b)
 end
 
+operate_to!(out::BigInt, ::typeof(-), a::BigInt) = Base.GMP.MPZ.neg!(out, a)
+
+operate!(::typeof(-), a::BigInt) = operate_to!(a, -, a)
+
 # *
 
 promote_operation(::typeof(*), ::Type{BigInt}, ::Type{BigInt}) = BigInt
@@ -49,6 +57,10 @@ function operate_to!(output::BigInt, ::typeof(*), a::BigInt, b::BigInt)
     return Base.GMP.MPZ.mul!(output, a, b)
 end
 
+operate_to!(out::BigInt, ::typeof(*), a::BigInt) = operate_to!(out, copy, a)
+
+operate!(::typeof(*), a::BigInt) = a
+
 promote_operation(::typeof(div), ::Type{BigInt}, ::Type{BigInt}) = BigInt
 
 function operate_to!(output::BigInt, ::typeof(div), a::BigInt, b::BigInt)
diff --git a/src/implementations/Rational.jl b/src/implementations/Rational.jl
index 2c293138..4e2c4a78 100644
--- a/src/implementations/Rational.jl
+++ b/src/implementations/Rational.jl
@@ -118,6 +118,23 @@ function operate_to!(output::Rational, ::typeof(+), x::Rational, y::Rational)
     return output
 end
 
+function operate_to!(out::Q, ::typeof(+), x::Q) where {Q<:Rational}
+    return operate_to!(out, copy, x)
+end
+
+operate!(::typeof(+), x::Rational) = x
+
+function operate_to!(out::Q, ::typeof(-), x::Q) where {Q<:Rational}
+    operate_to!(out.num, -, x.num)
+    operate_to!(out.den, copy, x.den)
+    return out
+end
+
+function operate!(::typeof(-), x::Rational)
+    operate!(-, x.num)
+    return x
+end
+
 # *
 
 function promote_operation(
@@ -162,6 +179,12 @@ function operate_to!(output::Rational, ::typeof(*), x::Rational, y::Rational)
     )
 end
 
+function operate_to!(out::Q, ::typeof(*), x::Q) where {Q<:Rational}
+    return operate_to!(out, copy, x)
+end
+
+operate!(::typeof(*), x::Rational) = x
+
 # gcd
 
 function promote_operation(
diff --git a/test/interface.jl b/test/interface.jl
index bfbfc8e9..8c7388e6 100644
--- a/test/interface.jl
+++ b/test/interface.jl
@@ -126,3 +126,26 @@ end
     @test MA.similar_array_type(BitArray{2}, Int) == Array{Int,2}
     @test MA.similar_array_type(BitArray{2}, Bool) == BitArray{2}
 end
+
+@testset "unary op(::$T)" for T in (
+    Float64,
+    BigFloat,
+    Int,
+    BigInt,
+    Rational{Int},
+    Rational{BigInt},
+)
+    @test MA.operate!!(+, T(7)) == 7
+    @test MA.operate!!(*, T(7)) == 7
+    @test MA.operate!!(-, T(7)) == -7
+
+    @test MA.operate_to!!(T(6), +, T(7)) == 7
+    @test MA.operate_to!!(T(6), *, T(7)) == 7
+    @test MA.operate_to!!(T(6), -, T(7)) == -7
+
+    @test MA.operate!!(abs, T(7)) == 7
+    @test MA.operate!!(abs, T(-7)) == 7
+
+    @test MA.operate_to!!(T(6), abs, T(7)) == 7
+    @test MA.operate_to!!(T(6), abs, T(-7)) == 7
+end