diff --git a/src/bson.jl b/src/bson.jl
index bdbfb2a..5c652a2 100644
--- a/src/bson.jl
+++ b/src/bson.jl
@@ -4,10 +4,10 @@
 #
 
 # BSONType mirrors C enum bson_type_t.
-primitive type BSONType 8 end # 1 byte
+primitive type BSONType sizeof(Cint) * 8 end
 
-Base.convert(::Type{T}, t::BSONType) where {T<:Number} = reinterpret(UInt8, t)
-Base.convert(::Type{BSONType}, n::T) where {T<:Number} = reinterpret(BSONType, n)
+Base.convert(::Type{T}, t::BSONType) where {T<:Number} = T(reinterpret(Cint, t))
+Base.convert(::Type{BSONType}, n::T) where {T<:Number} = reinterpret(BSONType, Cint(n))
 BSONType(u::UInt8) = convert(BSONType, u)
 
 #
@@ -40,10 +40,10 @@ const BSON_TYPE_MINKEY     = BSONType(0xFF)
 
 
 # BSONSubType mirrors C enum bson_subtype_t.
-primitive type BSONSubType 8 end
+primitive type BSONSubType sizeof(Cint) * 8 end
 
-Base.convert(::Type{T}, t::BSONSubType) where {T<:Number} = reinterpret(UInt8, t)
-Base.convert(::Type{BSONSubType}, n::T) where {T<:Number} = reinterpret(BSONSubType, n)
+Base.convert(::Type{T}, t::BSONSubType) where {T<:Number} = T(reinterpret(Cint, t))
+Base.convert(::Type{BSONSubType}, n::T) where {T<:Number} = reinterpret(BSONSubType, Cint(n))
 BSONSubType(u::UInt8) = convert(BSONSubType, u)
 
 #
diff --git a/test/bson_tests.jl b/test/bson_tests.jl
index a35b71c..4751827 100644
--- a/test/bson_tests.jl
+++ b/test/bson_tests.jl
@@ -113,6 +113,26 @@ using Distributed
         @test bson["uuid2"] == uuid
     end
 
+    @testset "Binary data iteration (#145)" begin
+        # This would segfault on Julia 1.12 before the enum size fix
+        b = Mongoc.BSON("a" => UInt8[0x1, 0x2, 0x3])
+
+        # Test iteration
+        result = iterate(b)
+        @test result !== nothing
+        (pair, state) = result
+        @test pair.first == "a"
+        @test pair.second == UInt8[0x1, 0x2, 0x3]
+
+        # Test Dict conversion (uses iteration internally)
+        d = Dict(b)
+        @test d["a"] == UInt8[0x1, 0x2, 0x3]
+
+        # Test as_dict
+        d2 = Mongoc.as_dict(b)
+        @test d2["a"] == UInt8[0x1, 0x2, 0x3]
+    end
+
     @testset "BSON key/values itr support" begin
         bson = Mongoc.BSON()
         bson["hey"] = 10