diff --git a/src/BitFlags.jl b/src/BitFlags.jl
index 2eec7f3..43533fb 100644
--- a/src/BitFlags.jl
+++ b/src/BitFlags.jl
@@ -16,9 +16,9 @@ abstract type BitFlag{T<:Integer} end
 
 basetype(::Type{<:BitFlag{T}}) where {T<:Integer} = T
 
-(::Type{T})(x::BitFlag{T2}) where {T<:Integer,T2<:Unsigned} = T(bitcast(T2, x))::T
-Base.cconvert(::Type{T}, x::BitFlag{T2}) where {T<:Unsigned,T2<:Unsigned} = T(x)
-Base.write(io::IO, x::BitFlag{T}) where {T<:Unsigned} = write(io, T(x))
+(::Type{T})(x::BitFlag{T2}) where {T<:Integer, T2} = T(bitcast(T2, x))::T
+Base.cconvert(::Type{T}, x::BitFlag{T2}) where {T<:Integer, T2} = T(T2(x))
+Base.write(io::IO, x::BitFlag{T}) where {T} = write(io, T(x))
 Base.read(io::IO, ::Type{T}) where {T<:BitFlag} = T(read(io, basetype(T)))
 
 Base.isless(x::T, y::T) where {T<:BitFlag} = isless(basetype(T)(x), basetype(T)(y))
diff --git a/test/runtests.jl b/test/runtests.jl
index 7fecfaa..14f8428 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -69,6 +69,22 @@ end
 
     # Broadcasting
     @test [flag1a, flag1b] .| flag1c == [flag1a | flag1c, flag1b | flag1c]
+
+    # ccall conversion
+    @bitflag CFlag1::UInt64 begin
+        cflag1_small = 1
+        cflag1_large = UInt64(1) << 63
+    end
+    flag_nonzero(x::Integer) = Cint(!iszero(x))
+    cflag_nonzero_u64 = @cfunction(flag_nonzero, Cint, (UInt64,))
+    cflag_nonzero_u32 = @cfunction(flag_nonzero, Cint, (UInt32,))
+    cflag_nonzero_i32 = @cfunction(flag_nonzero, Cint, (Int32,))
+    @test ccall(cflag_nonzero_u64, Cint, (UInt64,), cflag1_small) == 1
+    @test ccall(cflag_nonzero_u32, Cint, (UInt32,), cflag1_small) == 1
+    @test ccall(cflag_nonzero_i32, Cint, (Int32,), cflag1_small) == 1
+    @test ccall(cflag_nonzero_u64, Cint, (UInt64,), cflag1_large) == 1
+    @test_throws InexactError ccall(cflag_nonzero_u32, Cint, (UInt32,), cflag1_large)
+    @test_throws InexactError ccall(cflag_nonzero_i32, Cint, (Int32,), cflag1_large)
 #end
 
 #@testset "Type properties" begin