diff --git a/.gitignore b/.gitignore
index 4c0397994d..54ccae9e8c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -66,3 +66,6 @@ cmake/macro-conf/*.cmakedef
 
 # AI tooling items to ignore:
 CLAUDE.md
+
+# macOS specific items to ignore:
+*.DS_Store
diff --git a/bases/cmake-native/macos-arm/clang/lib/predefined_macros.txt b/bases/cmake-native/macos-arm/clang/lib/predefined_macros.txt
index 069b4a09c1..142d5612e8 100644
--- a/bases/cmake-native/macos-arm/clang/lib/predefined_macros.txt
+++ b/bases/cmake-native/macos-arm/clang/lib/predefined_macros.txt
@@ -111,7 +111,6 @@ clang no  __ATOMIC_RELEASE 3
 clang no  __ATOMIC_SEQ_CST 5
 clang no  __BIGGEST_ALIGNMENT__ 8
 clang no  __BITINT_MAXWIDTH__ 128
-clang no  __BLOCKS__ 1
 clang no  __BOOL_WIDTH__ 8
 clang no  __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 clang no  __CHAR_BIT__ 8
@@ -439,7 +438,6 @@ clang no  __aarch64__ 1
 clang no  __apple_build_version__ 15000309
 clang no  __arm64 1
 clang no  __arm64__ 1
-clang no  __block __attribute__((__blocks__(byref)))
 clang no  __clang_literal_encoding__ "UTF-8"
 clang no  __clang_wide_literal_encoding__ "UTF-32"
 clang no  __llvm__ 1
diff --git a/bases/cmake-native/macos-arm/clang/lib_macos_arm64/predefined_macros.txt b/bases/cmake-native/macos-arm/clang/lib_macos_arm64/predefined_macros.txt
index 069b4a09c1..142d5612e8 100644
--- a/bases/cmake-native/macos-arm/clang/lib_macos_arm64/predefined_macros.txt
+++ b/bases/cmake-native/macos-arm/clang/lib_macos_arm64/predefined_macros.txt
@@ -111,7 +111,6 @@ clang no  __ATOMIC_RELEASE 3
 clang no  __ATOMIC_SEQ_CST 5
 clang no  __BIGGEST_ALIGNMENT__ 8
 clang no  __BITINT_MAXWIDTH__ 128
-clang no  __BLOCKS__ 1
 clang no  __BOOL_WIDTH__ 8
 clang no  __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 clang no  __CHAR_BIT__ 8
@@ -439,7 +438,6 @@ clang no  __aarch64__ 1
 clang no  __apple_build_version__ 15000309
 clang no  __arm64 1
 clang no  __arm64__ 1
-clang no  __block __attribute__((__blocks__(byref)))
 clang no  __clang_literal_encoding__ "UTF-8"
 clang no  __clang_wide_literal_encoding__ "UTF-32"
 clang no  __llvm__ 1
diff --git a/bases/cmake-native/macos-x86_64/clang/lib/predefined_macros.txt b/bases/cmake-native/macos-x86_64/clang/lib/predefined_macros.txt
index 5398b421f9..bbdb1e76a2 100644
--- a/bases/cmake-native/macos-x86_64/clang/lib/predefined_macros.txt
+++ b/bases/cmake-native/macos-x86_64/clang/lib/predefined_macros.txt
@@ -62,7 +62,6 @@ clang no  __ATOMIC_RELAXED 0
 clang no  __ATOMIC_RELEASE 3
 clang no  __ATOMIC_SEQ_CST 5
 clang no  __BIGGEST_ALIGNMENT__ 16
-clang no  __BLOCKS__ 1
 clang no  __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 clang no  __CHAR_BIT__ 8
 clang no  __CLANG_ATOMIC_BOOL_LOCK_FREE 2
@@ -387,7 +386,6 @@ clang no  __WINT_WIDTH__ 32
 clang no  __amd64 1
 clang no  __amd64__ 1
 clang no  __apple_build_version__ 12050022
-clang no  __block __attribute__((__blocks__(byref)))
 clang no  __code_model_small__ 1
 clang no  __core2 1
 clang no  __core2__ 1
diff --git a/bases/cmake-native/macos-x86_64/clang/lib_macos_x86_64/predefined_macros.txt b/bases/cmake-native/macos-x86_64/clang/lib_macos_x86_64/predefined_macros.txt
index 5398b421f9..bbdb1e76a2 100644
--- a/bases/cmake-native/macos-x86_64/clang/lib_macos_x86_64/predefined_macros.txt
+++ b/bases/cmake-native/macos-x86_64/clang/lib_macos_x86_64/predefined_macros.txt
@@ -62,7 +62,6 @@ clang no  __ATOMIC_RELAXED 0
 clang no  __ATOMIC_RELEASE 3
 clang no  __ATOMIC_SEQ_CST 5
 clang no  __BIGGEST_ALIGNMENT__ 16
-clang no  __BLOCKS__ 1
 clang no  __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 clang no  __CHAR_BIT__ 8
 clang no  __CLANG_ATOMIC_BOOL_LOCK_FREE 2
@@ -387,7 +386,6 @@ clang no  __WINT_WIDTH__ 32
 clang no  __amd64 1
 clang no  __amd64__ 1
 clang no  __apple_build_version__ 12050022
-clang no  __block __attribute__((__blocks__(byref)))
 clang no  __code_model_small__ 1
 clang no  __core2 1
 clang no  __core2__ 1
diff --git a/tests/tests/changes/.GH307.rto/default.1.1.txt b/tests/tests/changes/.GH307.rto/default.1.1.txt
new file mode 100644
index 0000000000..33bda4bcb8
--- /dev/null
+++ b/tests/tests/changes/.GH307.rto/default.1.1.txt
@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 --clang Test_name.c
diff --git a/tests/tests/changes/GH307.sft.cpp b/tests/tests/changes/GH307.sft.cpp
new file mode 100644
index 0000000000..83ea1b2da2
--- /dev/null
+++ b/tests/tests/changes/GH307.sft.cpp
@@ -0,0 +1,28 @@
+//type:fp
+//options:--clang
+//remark:[GH #307] The macOS clang bases no longer predefine __BLOCKS__ and __block
+//
+// The front end does not support Apple's blocks extension (there is no block
+// pointer type, and "^" cannot start a declarator), so __BLOCKS__ must not be
+// predefined: the macOS SDK headers declare their block-taking functions
+// (atexit_b, bsearch_b, qsort_b, ...) under "#ifdef __BLOCKS__", and every
+// translation unit that included <stdlib.h> got errors.
+
+// The declaration that failed to parse.
+#if __BLOCKS__
+int atexit_b(void (^)(void));
+#endif
+
+#ifdef __BLOCKS__
+#error "__BLOCKS__ is defined"
+#endif
+
+#ifdef __block
+#error "__block is defined"
+#endif
+
+#if __has_feature(blocks) || __has_extension(blocks)
+#error "the front end does not support blocks"
+#endif
+
+int main() { return 0; }
diff --git a/util/Changes b/util/Changes
index a61673b293..2b5d271878 100644
--- a/util/Changes
+++ b/util/Changes
@@ -1,3 +1,19 @@
+Version 7.1
+
+10/15/26  [GH #307]
+Suppress the blocks macros in make_predef_macro_table output
+
+The __BLOCKS__ and __block macros are now suppressed when running
+make_predef_macro_table with --clang (so these don't end up in a
+predefined_macros.txt file).  Clang defines them together when the blocks
+extension is enabled (the default for Apple clang), but the front end does not
+support that extension, and the system headers that test __BLOCKS__ (the macOS
+SDK declares atexit_b, qsort_b and others under it) would then use block
+pointer types.  They have also been removed from the predefined_macros.txt
+files of the macOS clang bases.
+
+
+-------------------------------------------------------------------------------
 Version 7.0, September 28, 2026
 
 9/27/26  [EDGcpfe/29061]
diff --git a/util/make_predef_macro_table b/util/make_predef_macro_table
index 2242f41103..63bf663002 100755
--- a/util/make_predef_macro_table
+++ b/util/make_predef_macro_table
@@ -119,6 +119,8 @@ delete_unneeded_entries()
     unneeded="$unneeded __clang_minor__"
     unneeded="$unneeded __clang_patchlevel__"
     unneeded="$unneeded __clang_version__"
+    unneeded="$unneeded __BLOCKS__"
+    unneeded="$unneeded __block"
   else
     unneeded="$unneeded __GNUC__"
     unneeded="$unneeded __GNUC_MINOR__"