diff --git a/CMakeLists.txt b/CMakeLists.txt
index caea48c5060..a3ef4474ad1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,13 @@
 cmake_minimum_required(VERSION 3.14...3.28) # for add_link_options and implicit target directories.
-project("llama.cpp" C CXX)
+
+# Only call project() when llama.cpp is the top-level build. When consumed as
+# a subdirectory, a second project() would re-run toolchain detection and can
+# override parent-project settings. See:
+# https://github.com/ggml-org/llama.cpp/issues/20415
+if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+    project("llama.cpp" C CXX)
+endif()
+
 include(CheckIncludeFileCXX)
 
 #set(CMAKE_WARN_DEPRECATED YES)
diff --git a/ggml/CMakeLists.txt b/ggml/CMakeLists.txt
index 8454eecde6e..41d568c59d6 100644
--- a/ggml/CMakeLists.txt
+++ b/ggml/CMakeLists.txt
@@ -6,7 +6,16 @@ cmake_minimum_required(VERSION 3.14...3.28) # for add_link_options and implicit
 if (POLICY CMP0194)
     cmake_policy(SET CMP0194 NEW)
 endif()
-project("ggml" C CXX ASM)
+
+# Only call project() when ggml is the top-level build. When consumed as a
+# subdirectory (FetchContent, CPM, etc.), a second project() would re-run
+# toolchain detection and can clobber parent-project settings such as
+# CMAKE_OSX_ARCHITECTURES, CMAKE_OSX_SYSROOT or CMAKE_ASM_COMPILER during
+# cross-compilation (iOS, Android NDK, arm64/x86_64 hosts).
+# See: https://github.com/ggml-org/llama.cpp/issues/20415
+if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+    project("ggml" C CXX ASM)
+endif()
 
 ### GGML Version
 set(GGML_VERSION_MAJOR 0)