diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index b6cb745..e237cb8 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -45,6 +45,16 @@
 #include "mbedtls/pem.h"
 #endif /* MBEDTLS_PEM_WRITE_C */
 
+/*
+ * For the currently used signature algorithms the buffer to store any signature
+ * must be at least of size MAX(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)
+ */
+#if MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_MPI_MAX_SIZE
+#define SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
+#else
+#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
+#endif
+
 void mbedtls_x509write_crt_init( mbedtls_x509write_cert *ctx )
 {
     memset( ctx, 0, sizeof( mbedtls_x509write_cert ) );
@@ -317,7 +327,7 @@
     size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
-    unsigned char sig[MBEDTLS_MPI_MAX_SIZE];
+    unsigned char sig[SIGNATURE_MAX_SIZE];
     unsigned char tmp_buf[2048];
     size_t sub_len = 0, pub_len = 0, sig_and_oid_len = 0, sig_len;
     size_t len = 0;
diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index 8dc39e7..0d62d1d 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -49,6 +49,16 @@
 #include "mbedtls/pem.h"
 #endif
 
+/*
+ * For the currently used signature algorithms the buffer to store any signature
+ * must be at least of size MAX(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)
+ */
+#if MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_MPI_MAX_SIZE
+#define SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
+#else
+#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
+#endif
+
 void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
 {
     memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
@@ -138,7 +148,7 @@
     size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
-    unsigned char sig[MBEDTLS_MPI_MAX_SIZE];
+    unsigned char sig[SIGNATURE_MAX_SIZE];
     unsigned char tmp_buf[2048];
     size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
     size_t len = 0;
diff --git a/programs/pkey/pk_sign.c b/programs/pkey/pk_sign.c
index 7354082..4696c7c 100644
--- a/programs/pkey/pk_sign.c
+++ b/programs/pkey/pk_sign.c
@@ -72,6 +72,16 @@
 }
 #endif
 
+/*
+ * For the currently used signature algorithms the buffer to store any signature
+ * must be at least of size MAX(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)
+ */
+#if MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_MPI_MAX_SIZE
+#define SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
+#else
+#define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
+#endif
+
 int main( int argc, char *argv[] )
 {
     FILE *f;
@@ -81,7 +91,7 @@
     mbedtls_entropy_context entropy;
     mbedtls_ctr_drbg_context ctr_drbg;
     unsigned char hash[32];
-    unsigned char buf[MBEDTLS_MPI_MAX_SIZE];
+    unsigned char buf[SIGNATURE_MAX_SIZE];
     char filename[512];
     const char *pers = "mbedtls_pk_sign";
     size_t olen = 0;