diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6ee17ba7..4179126f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,6 +13,16 @@ include(CMakePackageConfigHelpers)
 
 # Build options
 option(BUILD_SHARED_LIBS "Build shared library" OFF)
+
+# Optional Clang -fbounds-safety. Default OFF: OGG_*COUNTED_BY* macros in
+# ogg_bounds_safety.h are inert and the ABI/build is unchanged. When ON,
+# requires a Clang that provides -fbounds-safety / <ptrcheck.h>.
+option(OGG_ENABLE_FBOUNDS_SAFETY
+       "Enable Clang -fbounds-safety annotations (experimental toolchain)" OFF)
+if(OGG_ENABLE_FBOUNDS_SAFETY)
+  add_definitions(-DOGG_SUPPORT_FBOUNDS_SAFETY)
+  add_compile_options(-fbounds-safety)
+endif()
 if(APPLE)
     option(BUILD_FRAMEWORK "Build Framework bundle for OSX" OFF)
 endif()
@@ -69,6 +79,7 @@ configure_file(include/ogg/config_types.h.in include/ogg/config_types.h @ONLY)
 set(OGG_HEADERS
     ${CMAKE_CURRENT_BINARY_DIR}/include/ogg/config_types.h
     include/ogg/ogg.h
+    include/ogg/ogg_bounds_safety.h
     include/ogg/os_types.h
 )
 
diff --git a/include/ogg/Makefile.am b/include/ogg/Makefile.am
index 142699d3..da8faf48 100644
--- a/include/ogg/Makefile.am
+++ b/include/ogg/Makefile.am
@@ -2,5 +2,5 @@
 
 oggincludedir = $(includedir)/ogg
 
-ogginclude_HEADERS = ogg.h os_types.h
+ogginclude_HEADERS = ogg.h ogg_bounds_safety.h os_types.h
 nodist_ogginclude_HEADERS = config_types.h
diff --git a/include/ogg/ogg.h b/include/ogg/ogg.h
index c4325aa7..136a51ad 100644
--- a/include/ogg/ogg.h
+++ b/include/ogg/ogg.h
@@ -22,6 +22,7 @@ extern "C" {
 
 #include <stddef.h>
 #include <ogg/os_types.h>
+#include <ogg/ogg_bounds_safety.h>
 
 typedef struct {
   void *iov_base;
@@ -50,7 +51,12 @@ typedef struct {
    Ogg bitstream **********************************************************/
 
 typedef struct {
-  unsigned char   *body_data;    /* bytes from packet bodies */
+  /* body_storage is the capacity companion for body_data.
+   * Field order is preserved (pointer before size) for public ABI;
+   * update sites assign capacity before the pointer so counted-by
+   * invariants hold under optional -fbounds-safety builds.
+   */
+  unsigned char   * OGG_COUNTED_BY_OR_NULL(body_storage) body_data; /* bytes from packet bodies */
   long    body_storage;          /* storage elements allocated */
   long    body_fill;             /* elements stored; fill mark */
   long    body_returned;         /* elements of fill returned */
diff --git a/include/ogg/ogg_bounds_safety.h b/include/ogg/ogg_bounds_safety.h
new file mode 100644
index 00000000..75d1b2c1
--- /dev/null
+++ b/include/ogg/ogg_bounds_safety.h
@@ -0,0 +1,39 @@
+/* ogg_bounds_safety.h - portability macros for optional -fbounds-safety
+ *
+ * Copyright (c) 2026 Jeff Bindel
+ *
+ * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE.
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.
+ *
+ * When OGG_SUPPORT_FBOUNDS_SAFETY is defined (typically via
+ * -DOGG_SUPPORT_FBOUNDS_SAFETY and a Clang toolchain that implements
+ * -fbounds-safety), these macros expand to Clang bounds annotations.
+ * Otherwise they expand to nothing so default builds are unchanged.
+ *
+ * Pattern matches libwebp / libpng / giflib inert-macro
+ * -fbounds-safety adoption: annotations are inert unless explicitly enabled.
+ */
+
+#ifndef OGG_BOUNDS_SAFETY_H
+#define OGG_BOUNDS_SAFETY_H
+
+#ifdef OGG_SUPPORT_FBOUNDS_SAFETY
+
+#  include <ptrcheck.h>
+/* Non-ABI-breaking counted-by annotations for struct pointer members.
+ * Prefer OGG_COUNTED_BY_OR_NULL for pointers that may be NULL while the
+ * companion size field is zero (ogg_stream_state.body_data pattern).
+ */
+#  define OGG_COUNTED_BY(n) __counted_by(n)
+#  define OGG_COUNTED_BY_OR_NULL(n) __counted_by_or_null(n)
+
+#else /* !OGG_SUPPORT_FBOUNDS_SAFETY */
+
+#  define OGG_COUNTED_BY(n)
+#  define OGG_COUNTED_BY_OR_NULL(n)
+
+#endif /* OGG_SUPPORT_FBOUNDS_SAFETY */
+
+#endif /* OGG_BOUNDS_SAFETY_H */
diff --git a/src/framing.c b/src/framing.c
index 4034eb53..f36abe93 100644
--- a/src/framing.c
+++ b/src/framing.c
@@ -133,6 +133,7 @@ static void _ogg_crc_init(){
 int ogg_stream_init(ogg_stream_state *os,int serialno){
   if(os){
     memset(os,0,sizeof(*os));
+    /* counted_by: set capacity before pointer */
     os->body_storage=16*1024;
     os->lacing_storage=1024;
 
@@ -162,6 +163,9 @@ int ogg_stream_check(ogg_stream_state *os){
 int ogg_stream_clear(ogg_stream_state *os){
   if(os){
     if(os->body_data)_ogg_free(os->body_data);
+    /* counted_by clear order: drop pointer then capacity */
+    os->body_data=NULL;
+    os->body_storage=0;
     if(os->lacing_vals)_ogg_free(os->lacing_vals);
     if(os->granule_vals)_ogg_free(os->granule_vals);
 
@@ -196,6 +200,7 @@ static int _os_body_expand(ogg_stream_state *os,long needed){
       ogg_stream_clear(os);
       return -1;
     }
+    /* counted_by: set capacity before pointer */
     os->body_storage=body_storage;
     os->body_data=ret;
   }