diff --git a/ChangeLog.d/ecdsa-conversion-overflow.txt b/ChangeLog.d/ecdsa-conversion-overflow.txt
new file mode 100644
index 0000000..83b7f2f
--- /dev/null
+++ b/ChangeLog.d/ecdsa-conversion-overflow.txt
@@ -0,0 +1,6 @@
+Security
+   * Fix a stack buffer overflow in mbedtls_ecdsa_der_to_raw() and
+     mbedtls_ecdsa_raw_to_der() when the bits parameter is larger than the
+     largest supported curve. In some configurations with PSA disabled,
+     all values of bits are affected. This never happens in internal library
+     calls, but can affect applications that call these functions directly.
diff --git a/library/psa_util.c b/library/psa_util.c
index 4ccc5b0..679d00e 100644
--- a/library/psa_util.c
+++ b/library/psa_util.c
@@ -443,6 +443,9 @@
     if (raw_len != (2 * coordinate_len)) {
         return MBEDTLS_ERR_ASN1_INVALID_DATA;
     }
+    if (coordinate_len > sizeof(r)) {
+        return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
+    }
 
     /* Since raw and der buffers might overlap, dump r and s before starting
      * the conversion. */
@@ -561,6 +564,9 @@
     if (raw_size < coordinate_size * 2) {
         return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
     }
+    if (2 * coordinate_size > sizeof(raw_tmp)) {
+        return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
+    }
 
     /* Check that the provided input DER buffer has the right header. */
     ret = mbedtls_asn1_get_tag(&p, der + der_len, &data_len,
diff --git a/tests/suites/test_suite_psa_crypto_util.data b/tests/suites/test_suite_psa_crypto_util.data
index 807007b..c84a836 100644
--- a/tests/suites/test_suite_psa_crypto_util.data
+++ b/tests/suites/test_suite_psa_crypto_util.data
@@ -6,6 +6,16 @@
 depends_on:PSA_VENDOR_ECC_MAX_CURVE_BITS >= 256
 ecdsa_raw_to_der:256:"11111111111111111111111111111111111111111111111111111111111111112222222222222222222222222222222222222222222222222222222222222222":"304402201111111111111111111111111111111111111111111111111111111111111111022022222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
 
+# Check coordinates one byte larger than the largest supported curve.
+# If we add an even larger curve, this test case will fail in the full
+# configuration because mbedtls_ecdsa_raw_to_der() will return 0, and we'll
+# need to use larger data for this test case.
+ECDSA Raw -> DER, very large input (536-bit)
+ecdsa_raw_to_der:536:"1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111122222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":"30818a024311111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111024322222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
+
+ECDSA Raw -> DER, very large input (1016-bit)
+ecdsa_raw_to_der:1016:"1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111122222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":"30820102027f11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111027f22222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
+
 ECDSA Raw -> DER, 256bit, Null r
 depends_on:PSA_VENDOR_ECC_MAX_CURVE_BITS >= 256
 ecdsa_raw_to_der:256:"00000000000000000000000000000000000000000000000000000000000000002222222222222222222222222222222222222222222222222222222222222222":"30440220111111111111111111111111111111111111111111111111111111111111111102202222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_INVALID_DATA
@@ -58,6 +68,16 @@
 depends_on:PSA_VENDOR_ECC_MAX_CURVE_BITS >= 256
 ecdsa_der_to_raw:256:"30440220111111111111111111111111111111111111111111111111111111111111111102202222222222222222222222222222222222222222222222222222222222222222":"111111111111111111111111111111111111111111111111111111111111111122222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
 
+# Check coordinates one byte larger than the largest supported curve.
+# If we add an even larger curve, this test case will fail in the full
+# configuration because mbedtls_ecdsa_der_to_raw() will return 0, and we'll
+# need to use larger data for this test case.
+ECDSA DER -> Raw, very large input (536-bit)
+ecdsa_der_to_raw:536:"30818a024311111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111024322222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":"1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111122222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
+
+ECDSA DER -> Raw, very large input (1016-bit)
+ecdsa_der_to_raw:1016:"30820102027f11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111027f22222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":"1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111122222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_BUF_TOO_SMALL
+
 ECDSA DER -> Raw, 256bit, Wrong sequence tag
 depends_on:PSA_VENDOR_ECC_MAX_CURVE_BITS >= 256
 ecdsa_der_to_raw:256:"40440220111111111111111111111111111111111111111111111111111111111111111102202222222222222222222222222222222222222222222222222222222222222222":"11111111111111111111111111111111111111111111111111111111111111112222222222222222222222222222222222222222222222222222222222222222":MBEDTLS_ERR_ASN1_UNEXPECTED_TAG