diff --git a/Misc/NEWS.d/next/Build/2026-03-18-00-00-00.gh-issue-138114.PwrVec.rst b/Misc/NEWS.d/next/Build/2026-03-18-00-00-00.gh-issue-138114.PwrVec.rst
new file mode 100644
index 00000000000000..9d5929b6a3b4af
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2026-03-18-00-00-00.gh-issue-138114.PwrVec.rst
@@ -0,0 +1,3 @@
+Enable HACL* BLAKE2s SIMD128 vectorization on PowerPC64 (POWER8+) using
+AltiVec/VSX instructions. The HACL* library already contained a complete
+PowerPC64 vec128 implementation but CPython's configure never enabled it.
diff --git a/Modules/_hacl/ppc_altivec_fix.h b/Modules/_hacl/ppc_altivec_fix.h
new file mode 100644
index 00000000000000..1283e96b6edf94
--- /dev/null
+++ b/Modules/_hacl/ppc_altivec_fix.h
@@ -0,0 +1,32 @@
+/*
+ * PowerPC AltiVec bool keyword fix for HACL* BLAKE2 SIMD128.
+ *
+ * When GCC compiles with -maltivec, it makes "bool" a keyword meaning
+ * "__vector __bool int" (a 128-bit vector type). This conflicts with
+ * C99/C11 stdbool.h where bool means _Bool (a scalar type).
+ *
+ * The -Dbool=_Bool workaround does NOT work because altivec.h re-enables
+ * the keyword after the macro is defined. Instead, this header includes
+ * altivec.h first, then undefines the bool/true/false keywords and
+ * restores the C99 scalar definitions. Vector boolean types remain
+ * accessible via the explicit __vector __bool syntax.
+ *
+ * This header is force-included (-include) before HACL SIMD128 sources
+ * via LIBHACL_SIMD128_FLAGS in configure.ac.
+ */
+#ifndef PPC_ALTIVEC_BOOL_FIX_H
+#define PPC_ALTIVEC_BOOL_FIX_H
+
+#if defined(__ALTIVEC__) || defined(__VSX__)
+#include <altivec.h>
+
+#undef bool
+#undef true
+#undef false
+
+#define bool _Bool
+#define true 1
+#define false 0
+#endif /* __ALTIVEC__ || __VSX__ */
+
+#endif /* PPC_ALTIVEC_BOOL_FIX_H */
diff --git a/configure b/configure
index 23f24d51c79e1a..2cba3b1f91c1dd 100755
--- a/configure
+++ b/configure
@@ -32918,9 +32918,63 @@ printf "%s\n" "standard" >&6; }
     fi
 
 
+else case e in #(
+  e)
+            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -maltivec -mvsx" >&5
+printf %s "checking whether C compiler accepts -maltivec -mvsx... " >&6; }
+if test ${ax_cv_check_cflags__Werror__maltivec__mvsx+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e)
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS -Werror -maltivec -mvsx"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  ax_cv_check_cflags__Werror__maltivec__mvsx=yes
+else case e in #(
+  e) ax_cv_check_cflags__Werror__maltivec__mvsx=no ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags__Werror__maltivec__mvsx" >&5
+printf "%s\n" "$ax_cv_check_cflags__Werror__maltivec__mvsx" >&6; }
+if test "x$ax_cv_check_cflags__Werror__maltivec__mvsx" = xyes
+then :
+
+      LIBHACL_SIMD128_FLAGS="-maltivec -mvsx -flax-vector-conversions -Wno-return-type -include \$(srcdir)/Modules/_hacl/ppc_altivec_fix.h"
+
+
+printf "%s\n" "#define _Py_HACL_CAN_COMPILE_VEC128 1" >>confdefs.h
+
+
+      LIBHACL_BLAKE2_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128.o"
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for HACL* SIMD128 implementation" >&5
+printf %s "checking for HACL* SIMD128 implementation... " >&6; }
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: PowerPC AltiVec/VSX" >&5
+printf "%s\n" "PowerPC AltiVec/VSX" >&6; }
+
 else case e in #(
   e) : ;;
 esac
+fi
+
+   ;;
+esac
 fi
 
 fi
diff --git a/configure.ac b/configure.ac
index 635fce3f2e6fad..9d7f649133c1a3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8110,7 +8110,7 @@ fi
 if test "$ac_sys_system" != "Linux-android" -a "$ac_sys_system" != "WASI" || \
    { test -n "$ANDROID_API_LEVEL" && test "$ANDROID_API_LEVEL" -ge 28; }
 then
-  dnl This can be extended here to detect e.g. Power8, which HACL* should also support.
+  dnl Check for x86 SSE support (SIMD128)
   AX_CHECK_COMPILE_FLAG([-msse -msse2 -msse3 -msse4.1 -msse4.2],[
     [LIBHACL_SIMD128_FLAGS="-msse -msse2 -msse3 -msse4.1 -msse4.2"]
 
@@ -8129,7 +8129,20 @@ then
       AC_MSG_RESULT([standard])
     fi
 
-  ], [], [-Werror])
+  ], [
+    dnl x86 SSE not available; check for PowerPC AltiVec/VSX (Power8+).
+    dnl HACL* libintvector.h has a complete vec128 implementation for __powerpc64__.
+    AX_CHECK_COMPILE_FLAG([-maltivec -mvsx],[
+      [LIBHACL_SIMD128_FLAGS="-maltivec -mvsx -flax-vector-conversions -Wno-return-type -include \$(srcdir)/Modules/_hacl/ppc_altivec_fix.h"]
+
+      AC_DEFINE([_Py_HACL_CAN_COMPILE_VEC128], [1], [
+        HACL* library can compile SIMD128 implementations])
+
+      [LIBHACL_BLAKE2_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128.o"]
+      AC_MSG_CHECKING([for HACL* SIMD128 implementation])
+      AC_MSG_RESULT([PowerPC AltiVec/VSX])
+    ], [], [-Werror])
+  ], [-Werror])
 fi
 AC_SUBST([LIBHACL_SIMD128_FLAGS])
 AC_SUBST([LIBHACL_BLAKE2_SIMD128_OBJS])