diff --git a/intl/icu_capi/bindings/cpp/icu4x/diplomat_runtime.hpp b/intl/icu_capi/bindings/cpp/icu4x/diplomat_runtime.hpp
index 2ef428fe024b..2d036b1d4ea5 100644
--- a/intl/icu_capi/bindings/cpp/icu4x/diplomat_runtime.hpp
+++ b/intl/icu_capi/bindings/cpp/icu4x/diplomat_runtime.hpp
@@ -372,17 +372,21 @@ struct diplomat_c_span_convert {
   struct diplomat_c_span_convert<T, std::enable_if_t<std::is_same_v<T, span<const c_ty>>>> { \
     using type = diplomat::capi::Diplomat##name##View; \
   }; \
   template<typename T> \
   struct diplomat_c_span_convert<T, std::enable_if_t<std::is_same_v<T, span<c_ty>>>> { \
     using type = diplomat::capi::Diplomat##name##ViewMut; \
   }; \
 
+#if !defined(__sun) || !defined(_CHAR_IS_SIGNED)
+// int8_t and char are the same type on Solaris. Guard this definition to avoid
+// conflicts. https://github.com/rust-diplomat/diplomat/issues/1015
 MAKE_SLICE_CONVERTERS(I8, int8_t)
+#endif
 MAKE_SLICE_CONVERTERS(U8, uint8_t)
 MAKE_SLICE_CONVERTERS(I16, int16_t)
 MAKE_SLICE_CONVERTERS(U16, uint16_t)
 MAKE_SLICE_CONVERTERS(I32, int32_t)
 MAKE_SLICE_CONVERTERS(U32, uint32_t)
 MAKE_SLICE_CONVERTERS(I64, int64_t)
 MAKE_SLICE_CONVERTERS(U64, uint64_t)
 MAKE_SLICE_CONVERTERS(F32, float)
@@ -559,9 +563,9 @@ struct next_to_iter_helper {
   }
 
   std::shared_ptr<T> _ptr; // shared to satisfy the copyable requirement
   next_type _curr;
 };
 
 } // namespace diplomat
 } // namespace icu4x
-#endif
\ No newline at end of file
+#endif