diff --git a/CMakeLists.txt b/CMakeLists.txt
index 746b38a..39808f9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -185,7 +185,10 @@
 
 add_subdirectory(library)
 add_subdirectory(include)
-add_subdirectory(tinycrypt)
+
+if(USE_TINYCRYPT)
+    add_subdirectory(tinycrypt)
+endif()
 
 if(ENABLE_PROGRAMS)
     add_subdirectory(programs)
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 82d5e33..ec1df15 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -39,14 +39,16 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
+#define MBEDTLS_ERR_PLATFORM_FAULT_DETECTED      -0x0071 /**< A hardware fault was detected in a critical path. As a security precaution this should be treated as a potential physical attack */
+
+#if defined(MBEDTLS_PLATFORM_C)
+
 #if defined(MBEDTLS_HAVE_TIME)
 #include "platform_time.h"
 #endif
 
-#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
-#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
-#define MBEDTLS_ERR_PLATFORM_FAULT_DETECTED      -0x0071 /**< A fault was detected in a critical path, likely indicative of an active physical attack */
-
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -365,4 +367,6 @@
 }
 #endif
 
+#endif /* MBEDTLS_PLATFORM_C */
+
 #endif /* platform.h */
diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index c31847d..b2ad182 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -85,6 +85,8 @@
  * \{
  */
 /* Reminder: update x509_crt_verify_strings[] in library/x509_crt.c */
+/* Reminder: update X509_BADCERT_FI_EXTRA in library/x509_crt.c if using more
+ * that 24 bits */
 #define MBEDTLS_X509_BADCERT_EXPIRED             0x01  /**< The certificate validity has expired. */
 #define MBEDTLS_X509_BADCERT_REVOKED             0x02  /**< The certificate has been revoked (is on a CRL). */
 #define MBEDTLS_X509_BADCERT_CN_MISMATCH         0x04  /**< The certificate Common Name (CN) does not match with the expected CN. */
diff --git a/include/tinycrypt/ecc.h b/include/tinycrypt/ecc.h
index 0d1d9ec..df8f1df 100644
--- a/include/tinycrypt/ecc.h
+++ b/include/tinycrypt/ecc.h
@@ -73,7 +73,6 @@
  *
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_UECC_H__
 #define __TC_UECC_H__
 
@@ -535,4 +534,3 @@
 #endif
 
 #endif /* __TC_UECC_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/include/tinycrypt/ecc_dh.h b/include/tinycrypt/ecc_dh.h
index a2edb01..d87393d 100644
--- a/include/tinycrypt/ecc_dh.h
+++ b/include/tinycrypt/ecc_dh.h
@@ -71,7 +71,6 @@
  *  Security: The curve NIST p-256 provides approximately 128 bits of security.
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_ECC_DH_H__
 #define __TC_ECC_DH_H__
 
@@ -135,4 +134,3 @@
 #endif
 
 #endif /* __TC_ECC_DH_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/include/tinycrypt/ecc_dsa.h b/include/tinycrypt/ecc_dsa.h
index 55b9d43..f744319 100644
--- a/include/tinycrypt/ecc_dsa.h
+++ b/include/tinycrypt/ecc_dsa.h
@@ -80,7 +80,6 @@
  *          the signer's public key and the signature values (r and s).
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_ECC_DSA_H__
 #define __TC_ECC_DSA_H__
 
@@ -143,4 +142,3 @@
 #endif
 
 #endif /* __TC_ECC_DSA_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 89f7275..0156856 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -1,4 +1,5 @@
 option(USE_STATIC_MBEDTLS_LIBRARY "Build mbed TLS static library." ON)
+option(USE_TINYCRYPT "Include TinyCrypt." ON)
 option(USE_SHARED_MBEDTLS_LIBRARY "Build mbed TLS shared library." OFF)
 option(LINK_WITH_PTHREAD "Explicitly link mbed TLS library to pthread." OFF)
 
@@ -123,7 +124,9 @@
     set(libs ${libs} pthread)
 endif()
 
-set(libs ${libs} tinycrypt)
+if(USE_TINYCRYPT)
+    set(libs ${libs} tinycrypt)
+endif()
 
 if (NOT USE_STATIC_MBEDTLS_LIBRARY AND NOT USE_SHARED_MBEDTLS_LIBRARY)
     message(FATAL_ERROR "Need to choose static or shared mbedtls build!")
diff --git a/library/Makefile b/library/Makefile
index 4154c6a..96a9d60 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -99,8 +99,7 @@
 		ripemd160.o	rsa_internal.o	rsa.o  		\
 		sha1.o		sha256.o	sha512.o	\
 		threading.o	timing.o	version.o	\
-		version_features.o		xtea.o		\
-		ecc.o		ecc_dh.o	ecc_dsa.o
+		version_features.o		xtea.o
 
 OBJS_X509=	certs.o		pkcs11.o	x509.o
 
@@ -110,6 +109,17 @@
 		ssl_srv.o	ssl_ticket.o		\
 		ssl_tls.o
 
+# Default to always build TinyCrypt
+ifndef TINYCRYPT_BUILD
+TINYCRYPT_BUILD=1
+endif
+
+ifeq ($(TINYCRYPT_BUILD),1)
+# Add TinyCrypt to the targets and Makefile path
+VPATH = ../tinycrypt
+OBJS_CRYPTO += ecc.o           ecc_dh.o        ecc_dsa.o
+endif
+
 .SILENT:
 
 .PHONY: all static shared clean
diff --git a/library/error.c b/library/error.c
index 77c7133..74c9d0b 100644
--- a/library/error.c
+++ b/library/error.c
@@ -842,7 +842,7 @@
     if( use_ret == -(MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED) )
         mbedtls_snprintf( buf, buflen, "PLATFORM - The requested feature is not supported by the platform" );
     if( use_ret == -(MBEDTLS_ERR_PLATFORM_FAULT_DETECTED) )
-        mbedtls_snprintf( buf, buflen, "PLATFORM - A fault was detected in a critical path, likely indicative of an active physical attack" );
+        mbedtls_snprintf( buf, buflen, "PLATFORM - A hardware fault was detected in a critical path. As a security precaution this should be treated as a potential physical attack" );
 #endif /* MBEDTLS_PLATFORM_C */
 
 #if defined(MBEDTLS_POLY1305_C)
diff --git a/library/x509_crt.c b/library/x509_crt.c
index e537983..fd3fa1a 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -43,6 +43,7 @@
 #include "mbedtls/x509_internal.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/platform.h"
 
 #include <string.h>
 
@@ -2884,6 +2885,10 @@
     return( 0 );
 }
 
+/* This value is different enough from 0 that it's hard for an active physical
+ * attacker to reach it just by flipping a few bits. */
+#define X509_SIGNATURE_IS_GOOD      0x7f5a5a5a
+
 /*
  * Find a suitable parent for child in candidates, or return NULL.
  *
@@ -2915,7 +2920,8 @@
  *  - [in] child: certificate for which we're looking for a parent
  *  - [in] candidates: chained list of potential parents
  *  - [out] r_parent: parent found (or NULL)
- *  - [out] r_signature_is_good: 1 if child signature by parent is valid, or 0
+ *  - [out] r_signature_is_good: set to X509_SIGNATURE_IS_GOOD if
+ *                               child signature by parent is valid, or to 0
  *  - [in] top: 1 if candidates consists of trusted roots, ie we're at the top
  *         of the chain, 0 otherwise
  *  - [in] path_cnt: number of intermediates seen so far
@@ -2938,8 +2944,9 @@
                         mbedtls_x509_crt_restart_ctx *rs_ctx )
 {
     int ret;
+    volatile int ret_fi = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
     mbedtls_x509_crt *parent_crt;
-    int signature_is_good;
+    int signature_is_good = 0;
 
 #if defined(MBEDTLS_HAVE_TIME_DATE)
     mbedtls_x509_crt *fallback_parent;
@@ -3018,10 +3025,10 @@
             continue;
 
         /* Signature */
-        ret = x509_crt_check_signature( child_sig, parent_crt, rs_ctx );
+        ret_fi = x509_crt_check_signature( child_sig, parent_crt, rs_ctx );
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
-        if( rs_ctx != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
+        if( rs_ctx != NULL && ret_fi == MBEDTLS_ERR_ECP_IN_PROGRESS )
         {
             /* save state */
             rs_ctx->parent = parent_crt;
@@ -3030,13 +3037,17 @@
             rs_ctx->fallback_signature_is_good = fallback_signature_is_good;
 #endif /* MBEDTLS_HAVE_TIME_DATE */
 
-            return( ret );
+            return( ret_fi );
         }
-#else
-        (void) ret;
 #endif
 
-        signature_is_good = ret == 0;
+        if( ret_fi == 0 )
+        {
+            mbedtls_platform_enforce_volatile_reads();
+            if( ret_fi == 0 )
+                signature_is_good = X509_SIGNATURE_IS_GOOD;
+        }
+
         if( top && ! signature_is_good )
             continue;
 
@@ -3318,6 +3329,23 @@
 #endif /* MBEDTLS_X509_REMOVE_VERIFY_CALLBACK */
 
 /*
+ * This is used in addition to the flag for a specific issue, to ensure that
+ * it is not possible for an active physical attacker to entirely clear the
+ * flags just by flipping a single bit. Take advantage of the fact that all
+ * values defined in include/mbedtls/x509.h so far are 24-bit or less, so the
+ * top byte is free.
+ *
+ * Currently this protection is not compatible with the vrfy callback (as it
+ * can observ and modify flags freely), so it's only enabled when the callback
+ * is disabled.
+ */
+#if defined(MBEDTLS_X509_REMOVE_VERIFY_CALLBACK)
+#define X509_BADCERT_FI_EXTRA   0xff000000u
+#else
+#define X509_BADCERT_FI_EXTRA   0u
+#endif
+
+/*
  * Build and verify a certificate chain
  *
  * Given a peer-provided list of certificates EE, C1, ..., Cn and
@@ -3374,6 +3402,7 @@
     int parent_is_trusted;
     int child_is_trusted;
     int signature_is_good;
+    volatile int signature_is_good_fi;
     unsigned self_cnt;
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
@@ -3422,9 +3451,9 @@
 #if !defined(MBEDTLS_X509_CRT_REMOVE_TIME)
                 /* Check time-validity (all certificates) */
                 if( mbedtls_x509_time_is_past( &child->valid_to ) )
-                    *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
+                    *flags |= MBEDTLS_X509_BADCERT_EXPIRED | X509_BADCERT_FI_EXTRA;
                 if( mbedtls_x509_time_is_future( &child->valid_from ) )
-                    *flags |= MBEDTLS_X509_BADCERT_FUTURE;
+                    *flags |= MBEDTLS_X509_BADCERT_FUTURE | X509_BADCERT_FI_EXTRA;
 #endif /* !MBEDTLS_X509_CRT_REMOVE_TIME */
 
                 /* Stop here for trusted roots (but not for trusted EE certs) */
@@ -3444,10 +3473,10 @@
 
                 /* Check signature algorithm: MD & PK algs */
                 if( x509_profile_check_md_alg( profile, child->sig_md ) != 0 )
-                    *flags |= MBEDTLS_X509_BADCERT_BAD_MD;
+                    *flags |= MBEDTLS_X509_BADCERT_BAD_MD | X509_BADCERT_FI_EXTRA;
 
                 if( x509_profile_check_pk_alg( profile, child->sig_pk ) != 0 )
-                    *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+                    *flags |= MBEDTLS_X509_BADCERT_BAD_PK | X509_BADCERT_FI_EXTRA;
 
                 /* Special case: EE certs that are locally trusted */
                 if( x509_crt_verify_chain_len( ver_chain ) == 1 && self_issued &&
@@ -3495,7 +3524,7 @@
         /* No parent? We're done here */
         if( parent_crt == NULL )
         {
-            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
             return( 0 );
         }
 
@@ -3516,8 +3545,13 @@
         }
 
         /* signature was checked while searching parent */
-        if( ! signature_is_good )
-            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+        signature_is_good_fi = signature_is_good;
+        if( signature_is_good_fi != X509_SIGNATURE_IS_GOOD )
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
+
+        mbedtls_platform_enforce_volatile_reads();
+        if( signature_is_good_fi != X509_SIGNATURE_IS_GOOD )
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
 
         {
             mbedtls_pk_context *parent_pk;
@@ -3527,7 +3561,7 @@
 
             /* check size of signing key */
             if( x509_profile_check_key( profile, parent_pk ) != 0 )
-                *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+                *flags |= MBEDTLS_X509_BADCERT_BAD_KEY | X509_BADCERT_FI_EXTRA;
 
             mbedtls_x509_crt_pk_release( parent_crt );
         }
@@ -3658,7 +3692,7 @@
     if( ret != 0 )
         ret = MBEDTLS_ERR_X509_FATAL_ERROR;
 
-    *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
+    *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH | X509_BADCERT_FI_EXTRA;
     return( ret );
 }
 #endif /* !MBEDTLS_X509_REMOVE_HOSTNAME_VERIFICATION */
@@ -3747,6 +3781,7 @@
     int ret;
     mbedtls_x509_crt_verify_chain ver_chain;
     uint32_t ee_flags;
+    volatile uint32_t flags_fi = (uint32_t) -1;
 
     *flags = 0;
     ee_flags = 0;
@@ -3780,10 +3815,10 @@
         pk_type = mbedtls_pk_get_type( pk );
 
         if( x509_profile_check_pk_alg( profile, pk_type ) != 0 )
-            ee_flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+            ee_flags |= MBEDTLS_X509_BADCERT_BAD_PK | X509_BADCERT_FI_EXTRA;
 
         if( x509_profile_check_key( profile, pk ) != 0 )
-            ee_flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+            ee_flags |= MBEDTLS_X509_BADCERT_BAD_KEY | X509_BADCERT_FI_EXTRA;
 
         mbedtls_x509_crt_pk_release( crt );
     }
@@ -3823,10 +3858,19 @@
         return( ret );
     }
 
-    if( *flags != 0 )
-        return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
+    flags_fi = *flags;
+    if( flags_fi == 0 )
+    {
+        mbedtls_platform_enforce_volatile_reads();
+        if( flags_fi == 0 )
+            return( 0 );
+    }
 
-    return( 0 );
+    /* Preserve the API by removing internal extra bits - from now on the
+     * fact that flags is non-zero is also redundantly encoded by the
+     * non-zero return value from this function. */
+    *flags &= ~ X509_BADCERT_FI_EXTRA;
+    return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
 }
 
 /*
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 02f96a9..42ef32d 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1491,7 +1491,7 @@
     msg "build: arm-none-eabi-gcc MBEDTLS_NO_64BIT_MULTIPLICATION, make" # ~ 10s
     scripts/config.pl baremetal
     scripts/config.pl set MBEDTLS_NO_64BIT_MULTIPLICATION
-    make CC=arm-none-eabi-gcc AR=arm-none-eabi-ar LD=arm-none-eabi-ld CFLAGS='-Werror -O1 -march=armv6-m -mthumb' lib
+    make TINYCRYPT_BUILD=0 CC=arm-none-eabi-gcc AR=arm-none-eabi-ar LD=arm-none-eabi-ld CFLAGS='-Werror -O1 -march=armv6-m -mthumb' lib
     echo "Checking that software 64-bit multiplication is not required"
     if_build_succeeded not grep __aeabi_lmul library/*.o
 }
diff --git a/tests/scripts/list-symbols.sh b/tests/scripts/list-symbols.sh
index 930722c..12b3281 100755
--- a/tests/scripts/list-symbols.sh
+++ b/tests/scripts/list-symbols.sh
@@ -16,7 +16,7 @@
 scripts/config.pl full
 make clean
 make_ret=
-CFLAGS=-fno-asynchronous-unwind-tables make lib \
+CFLAGS=-fno-asynchronous-unwind-tables TINYCRYPT_BUILD=0 make lib \
       >list-symbols.make.log 2>&1 ||
   {
     make_ret=$?
diff --git a/tinycrypt/ecc.c b/tinycrypt/ecc.c
index 92906fd..38b11d9 100644
--- a/tinycrypt/ecc.c
+++ b/tinycrypt/ecc.c
@@ -63,7 +63,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include "mbedtls/platform_util.h"
 #include <string.h>
@@ -1114,7 +1113,4 @@
 	curve->num_bytes, curve->num_bytes, _public + curve->num_words);
 	return 1;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */
 
diff --git a/tinycrypt/ecc_dh.c b/tinycrypt/ecc_dh.c
index f9c0a5e..3ab7b15 100644
--- a/tinycrypt/ecc_dh.c
+++ b/tinycrypt/ecc_dh.c
@@ -66,7 +66,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include <tinycrypt/ecc_dh.h>
 #include <string.h>
@@ -188,6 +187,3 @@
 
 	return r;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/tinycrypt/ecc_dsa.c b/tinycrypt/ecc_dsa.c
index 6c171c3..67b33a4 100644
--- a/tinycrypt/ecc_dsa.c
+++ b/tinycrypt/ecc_dsa.c
@@ -64,7 +64,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include <tinycrypt/ecc_dsa.h>
 #include "mbedtls/platform_util.h"
@@ -316,6 +315,3 @@
 
 	return UECC_FAILURE;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */