diff --git a/foundation-models-c/Sources/FoundationModelsCBindings/FoundationModelsCBindings.swift b/foundation-models-c/Sources/FoundationModelsCBindings/FoundationModelsCBindings.swift
index b58917b..174da41 100644
--- a/foundation-models-c/Sources/FoundationModelsCBindings/FoundationModelsCBindings.swift
+++ b/foundation-models-c/Sources/FoundationModelsCBindings/FoundationModelsCBindings.swift
@@ -9,7 +9,10 @@ import FoundationModelsCDeclarations
 import Synchronization
 
 enum ComposedPromptError: Error {
-  case unsupported
+  // Error thrown when the SDK, at build time, does not support attachments
+  case unsupportedSDK
+  // Error thrown when the runtime OS does not support attachments
+  case unsupportedOS
 }
 
 /// Builder class for a `Prompt`.
@@ -36,10 +39,12 @@ public class ComposedPrompt: NSObject, PromptRepresentable {
       }
       self.components.append(attachment)
       return
+    } else {
+      throw ComposedPromptError.unsupportedOS
     }
+    #else
+    throw ComposedPromptError.unsupportedSDK
     #endif
-
-    throw ComposedPromptError.unsupported
   }
 
   public var promptRepresentation: Prompt {
@@ -74,8 +79,11 @@ public func FMComposedPromptAddAttachment(
   do {
     try composedPrompt.add(attachmentFromPath: imageURLToAddToPrompt, label: labelString)
     return true
-  } catch ComposedPromptError.unsupported {
-    error?.pointee = FMComposedPromptAddImageErrorUnsupported
+  } catch ComposedPromptError.unsupportedOS {
+    error?.pointee = FMComposedPromptAddImageErrorUnsupportedOS
+    return false
+  } catch ComposedPromptError.unsupportedSDK {
+    error?.pointee = FMComposedPromptAddImageErrorUnsupportedSDK
     return false
   } catch _ {
     error?.pointee = FMComposedPromptAddImageErrorUnknown
diff --git a/foundation-models-c/Sources/FoundationModelsCBindings/include/FoundationModels.h b/foundation-models-c/Sources/FoundationModelsCBindings/include/FoundationModels.h
index 91db347..29c13d5 100644
--- a/foundation-models-c/Sources/FoundationModelsCBindings/include/FoundationModels.h
+++ b/foundation-models-c/Sources/FoundationModelsCBindings/include/FoundationModels.h
@@ -64,7 +64,8 @@ FMComposedPrompt _Nonnull FMComposedPromptInitialize();
 
 typedef enum {
     FMComposedPromptAddImageErrorNone,
-    FMComposedPromptAddImageErrorUnsupported,
+    FMComposedPromptAddImageErrorUnsupportedOS,
+    FMComposedPromptAddImageErrorUnsupportedSDK,
     FMComposedPromptAddImageErrorUnknown
 } FMComposedPromptAddImageError;
 
diff --git a/src/apple_fm_sdk/prompt.py b/src/apple_fm_sdk/prompt.py
index a3a9300..0414147 100644
--- a/src/apple_fm_sdk/prompt.py
+++ b/src/apple_fm_sdk/prompt.py
@@ -3,9 +3,6 @@
 
 from abc import ABC, abstractmethod
 import logging
-from .c_helpers import (
-    _get_error_string,
-)
 from typing import Optional, Union
 from pathlib import Path
 
@@ -15,6 +12,10 @@
 
 try:
     from . import _ctypes_bindings as lib
+    from ._ctypes_bindings import (
+        FMComposedPromptAddImageErrorUnsupportedOS,
+        FMComposedPromptAddImageErrorUnsupportedSDK,
+    )
 except ImportError:
     raise ImportError(
         "Foundation Models C bindings not found. Please ensure _foundationmodels_ctypes.py is available."
@@ -158,7 +159,8 @@ def add_to_composed_prompt(self, composed_prompt):
         :param composed_prompt: The native composed prompt object to add this attachment to
         :type composed_prompt: ctypes pointer
         :raises ImagePromptError: If the attachment cannot be added, either because
-            the image format is not supported or another error occurs
+            the runtime OS or the build-time SDK doesn't support attachments, or
+            another error occurs.
         """
         label_bytes = self._label.encode("utf-8") if self._label else None
         error_reason = ctypes.c_int()
@@ -168,11 +170,13 @@ def add_to_composed_prompt(self, composed_prompt):
             label_bytes,
             ctypes.byref(error_reason),
         ):
-            error = _get_error_string(error_reason, None)
-            error_message = error[1] if error[1] else "Attachment prompts not supported"
-            raise ImagePromptError(
-                f"Failed to add attachment to prompt: {error_message}"
-            )
+            if error_reason.value == FMComposedPromptAddImageErrorUnsupportedOS:
+                detail = "the current OS does not support attachment prompts"
+            elif error_reason.value == FMComposedPromptAddImageErrorUnsupportedSDK:
+                detail = "the Xcode version used to build this package doesn't include macOS 27 SDKs"
+            else:
+                detail = "an unknown error occurred while adding the attachment"
+            raise ImagePromptError(f"Failed to add attachment to prompt: {detail}")
 
 
 PromptComponent = Union[str, Attachment]
@@ -251,8 +255,9 @@ class ImagePromptError(PromptError):
     This exception is raised when there are issues with image attachments, such as:
 
     - Image file not found at the specified path
-    - Unsupported image format
-    - Failure to add the image to the prompt
+    - The current OS does not support attachment prompts
+    - The Xcode version used to build this package doesn't include the right SDKs for
+      image input support
 
     Examples:
         Handling image prompt errors::