diff --git a/src/Normaliz.jl b/src/Normaliz.jl
index 8e4fcc1..65174d3 100644
--- a/src/Normaliz.jl
+++ b/src/Normaliz.jl
@@ -22,6 +22,10 @@ function Base.convert(::Type{BigInt},x::NmzInteger)
     return result
 end
 Base.convert(::Type{NmzRational},x::Int64) = NmzRational(x,1)
+Base.convert(::Type{NmzRational},x::BigInt) =
+    NmzRational(convert(NmzInteger,x), NmzInteger(1))
+Base.convert(::Type{NmzRational},x::NmzInteger) =
+    NmzRational(x, NmzInteger(1))
 Base.://(x::NmzInteger,y::NmzInteger) = NmzRational(x,y)
 Base.convert(::Type{NmzRational},x::Rational{BigInt}) =
     convert(NmzInteger,x.num) // convert(NmzInteger,x.den)
@@ -99,17 +103,37 @@ get_boolean_cone_property(cone, property::Symbol) =
 function _normaliz_input(input::AbstractDict)
     input_pairs = collect(pairs(input))
     input_keys = String[]
-    for (key, _) in input_pairs
+    input_matrices = NmzMatrix{NmzRational}[]
+    for (key, matrix) in input_pairs
         key isa Symbol ||
             throw(ArgumentError("Normaliz cone input keys must be Symbols"))
         push!(input_keys, String(key))
+        push!(input_matrices, _normaliz_input_matrix(key, matrix))
     end
     input_keys = CxxWrap.StdLib.StdVector{CxxWrap.StdLib.StdString}(input_keys)
-    input_matrices = CxxRef.([matrix for (_, matrix) in input_pairs])
+    input_matrices = CxxRef.(input_matrices)
     return input_keys, input_matrices
 end
 
-function NmzMatrix{T}(x::Matrix{S}) where S where T
+_normaliz_input_matrix(key::Symbol, matrix::NmzMatrix{NmzRational}) = matrix
+
+function _normaliz_input_matrix(key::Symbol, matrix::AbstractMatrix)
+    try
+        return NmzMatrix{NmzRational}(matrix)
+    catch err
+        throw(ArgumentError(
+            "Normaliz cone input value for :$key must be convertible " *
+            "to NmzMatrix{NmzRational}"))
+    end
+end
+
+function _normaliz_input_matrix(key::Symbol, value)
+    throw(ArgumentError(
+        "Normaliz cone input values must be matrices; " *
+        "value for :$key has type $(typeof(value))"))
+end
+
+function NmzMatrix{T}(x::AbstractMatrix{S}) where S where T
    s = size(x)
    mat = NmzMatrix{T}(s[1],s[2])
    for i in 1:s[1], j in 1:s[2]
diff --git a/test/runtests.jl b/test/runtests.jl
index ec4ad58..91cb84b 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -60,6 +60,35 @@ end
   @test string(input_matrices[cone_index][][1, 1]) == "1/2"
   @test size(input_matrices[grading_index][]) == (1, 2)
 
+  input_keys, input_matrices = Normaliz._normaliz_input(
+      Dict(:cone => [1//2 2 ; 3 5], :grading => [1 1]))
+  input_key_strings = collect(input_keys)
+  cone_index = findfirst(==("cone"), input_key_strings)
+  grading_index = findfirst(==("grading"), input_key_strings)
+  @test input_matrices[cone_index][] isa Normaliz.NmzMatrix{Normaliz.NmzRational}
+  @test string(input_matrices[cone_index][][1, 1]) == "1/2"
+  @test size(input_matrices[grading_index][]) == (1, 2)
+
+  large_integer = big(2)^80 + 1
+  input_keys, input_matrices = Normaliz._normaliz_input(
+      Dict(:cone => BigInt[large_integer 2; 3 4]))
+  @test string(input_matrices[1][][1, 1]) == string(large_integer)
+
+  integer_matrix = Normaliz.NmzMatrix{Normaliz.NmzInteger}([1 2 ; 3 4])
+  input_keys, input_matrices = Normaliz._normaliz_input(Dict(:cone => integer_matrix))
+  @test input_matrices[1][] isa Normaliz.NmzMatrix{Normaliz.NmzRational}
+  @test string(input_matrices[1][][1, 1]) == "1"
+
+  yy = Normaliz.LongLongCone(Dict(:cone => [1//2 2 ; 3 5], :grading => [1 1]))
+  @test yy isa Normaliz.Cone
+
+  err = @test_throws ArgumentError Normaliz._normaliz_input(Dict(:cone => "not a matrix"))
+  @test occursin("cone", err.value.msg)
+  @test occursin("Normaliz cone input values", err.value.msg)
+
+  err = @test_throws ArgumentError Normaliz._normaliz_input(Dict(:cone => ["x" ;;]))
+  @test occursin("NmzRational", err.value.msg)
+
   mismatched_keys = CxxWrap.StdLib.StdVector{CxxWrap.StdLib.StdString}(["cone", "grading"])
   err = @test_throws ErrorException Normaliz._LongLongCone(mismatched_keys, input_matrices[1:1])
   @test err.value.msg == "Normaliz cone input keys and matrices must have the same length"