diff --git a/crypto/abi_self_test.cc b/crypto/abi_self_test.cc
index 9a1b868..7790ac5 100644
--- a/crypto/abi_self_test.cc
+++ b/crypto/abi_self_test.cc
@@ -174,6 +174,11 @@
   CHECK_ABI_NO_UNWIND(abi_test_clobber_xmm14);
   CHECK_ABI_NO_UNWIND(abi_test_clobber_xmm15);
 #endif
+
+  EXPECT_NONFATAL_FAILURE(CHECK_ABI_NO_UNWIND(abi_test_set_direction_flag),
+                          "Direction flag set after return");
+  EXPECT_EQ(0, abi_test_get_and_clear_direction_flag())
+      << "CHECK_ABI did not insulate the caller from direction flag errors";
 }
 
 #if defined(OPENSSL_WINDOWS)
diff --git a/crypto/test/abi_test.cc b/crypto/test/abi_test.cc
index e86f2f4..6530ddf 100644
--- a/crypto/test/abi_test.cc
+++ b/crypto/test/abi_test.cc
@@ -90,11 +90,25 @@
   unwind &= g_unwind_tests_enabled;
   CallerState state2 = state;
   crypto_word_t ret = abi_test_trampoline(func, &state2, argv, argc, unwind);
+#if defined(OPENSSL_X86_64) || defined(OPENSSL_X86)
+  // Query and clear the direction flag early, so negative tests do not
+  // interfere with |malloc|.
+  bool direction_flag = abi_test_get_and_clear_direction_flag();
+#endif  // OPENSSL_X86_64 || OPENSSL_X86
 
   *out = Result();
   ForEachMismatch(state, state2, [&](const char *reg) {
     out->errors.push_back(std::string(reg) + " was not restored after return");
   });
+#if defined(OPENSSL_X86_64) || defined(OPENSSL_X86)
+  // Linux and Windows ABIs for x86 require the direction flag be cleared on
+  // return. (Some OpenSSL assembly preserves it, which is stronger, but we only
+  // require what is specified by the ABI so |CHECK_ABI| works with C compiler
+  // output.)
+  if (direction_flag) {
+    out->errors.emplace_back("Direction flag set after return");
+  }
+#endif  // OPENSSL_X86_64 || OPENSSL_X86
   if (unwind) {
     ReadUnwindResult(out);
   }
diff --git a/crypto/test/abi_test.h b/crypto/test/abi_test.h
index 23f3aa5..370d455 100644
--- a/crypto/test/abi_test.h
+++ b/crypto/test/abi_test.h
@@ -286,6 +286,17 @@
 // storage space for a saved register, breaking unwind.
 void abi_test_bad_unwind_temporary(void);
 
+#if defined(OPENSSL_X86_64) || defined(OPENSSL_X86)
+// abi_test_get_and_clear_direction_flag clears the direction flag. If the flag
+// was previously set, it returns one. Otherwise, it returns zero.
+int abi_test_get_and_clear_direction_flag(void);
+
+// abi_test_set_direction_flag sets the direction flag. This does not conform to
+// ABI requirements and must only be called within a |CHECK_ABI| guard to avoid
+// errors later in the program.
+int abi_test_set_direction_flag(void);
+#endif  // OPENSSL_X86_64 || OPENSSL_X86
+
 }  // extern "C"
 #endif  // SUPPORTS_ABI_TEST
 
diff --git a/crypto/test/asm/trampoline-x86_64.pl b/crypto/test/asm/trampoline-x86_64.pl
index d41aadf..4af9b2a 100755
--- a/crypto/test/asm/trampoline-x86_64.pl
+++ b/crypto/test/asm/trampoline-x86_64.pl
@@ -366,6 +366,29 @@
 	ret
 .cfi_endproc
 .size	abi_test_bad_unwind_temporary,.-abi_test_bad_unwind_temporary
+
+# abi_test_get_and_clear_direction_flag clears the direction flag. If the flag
+# was previously set, it returns one. Otherwise, it returns zero.
+# int abi_test_get_and_clear_direction_flag(void);
+.type	abi_test_set_direction_flag, \@abi-omnipotent
+.globl	abi_test_get_and_clear_direction_flag
+abi_test_get_and_clear_direction_flag:
+	pushfq
+	popq	%rax
+	andq	\$0x400, %rax
+	shlq	\$10, %rax
+	cld
+	ret
+.size abi_test_get_and_clear_direction_flag,.-abi_test_get_and_clear_direction_flag
+
+# abi_test_set_direction_flag sets the direction flag.
+# void abi_test_set_direction_flag(void);
+.type	abi_test_set_direction_flag, \@abi-omnipotent
+.globl	abi_test_set_direction_flag
+abi_test_set_direction_flag:
+	std
+	ret
+.size abi_test_set_direction_flag,.-abi_test_set_direction_flag
 ____
 
 if ($win64) {