diff --git a/library/rsa.c b/library/rsa.c
index f25137a..b54960f 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -1371,15 +1371,15 @@
      */
     msb = mbedtls_mpi_bitlen( &ctx->N ) - 1;
 
+    if( buf[0] >> ( 8 - siglen * 8 + msb ) )
+        return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
+
     /* Compensate for boundary condition when applying mask */
     if( msb % 8 == 0 )
     {
         p++;
         siglen -= 1;
     }
-    else
-    if( buf[0] >> ( 8 - siglen * 8 + msb ) )
-        return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
 
     if( siglen < hlen + 2 )
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
diff --git a/tests/suites/test_suite_pkcs1_v21.data b/tests/suites/test_suite_pkcs1_v21.data
index 7785b12..6258c62 100644
--- a/tests/suites/test_suite_pkcs1_v21.data
+++ b/tests/suites/test_suite_pkcs1_v21.data
@@ -819,6 +819,14 @@
 depends_on:MBEDTLS_SHA512_C
 pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA512:MBEDTLS_MD_SHA512:MBEDTLS_MD_SHA512:0:"":"00471794655837da498cbf27242807b40593a353c707eb22fd2cc5a3259e728ac4f1df676043eeec8e16c1175b3d9ac8cae72ec1d5772dd69de71c5677f19031568e":MBEDTLS_ERR_RSA_BAD_INPUT_DATA:MBEDTLS_ERR_RSA_BAD_INPUT_DATA
 
+RSASSA-PSS verify ext, 521-bit key, SHA-256, empty salt, good signature
+depends_on:MBEDTLS_SHA256_C
+pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:0:"41":"009c4941157fa36288e467310b198ab0c615c40963d611ffeef03000549ded809235955ecc57adba44782e9497c004f480ba2b3d58db8335fe0b391075c02c843a6d":0:0
+
+RSASSA-PSS verify ext, 521-bit key, SHA-256, empty salt, flipped-highest-bit signature
+depends_on:MBEDTLS_SHA256_C
+pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:0:"41":"00e11a2403df681c44a1f73f014b6c9ad17847d0b673f7c2a801cee208d10ab5792c10cd0cd495a4b331aaa521409fca7cb1b0d978b3a84cd67e28078b98753e9466":MBEDTLS_ERR_RSA_BAD_INPUT_DATA:MBEDTLS_ERR_RSA_BAD_INPUT_DATA
+
 RSASSA-PSS verify ext, all-zero padding, automatic salt length
 depends_on:MBEDTLS_SHA256_C
 pkcs1_rsassa_pss_verify_ext:512:16:"00b076d23250816f9aab02307e452b97f0cae7598369b41624e8afc7971a59a13892f64b07eaa6ec928c160b2d6ec8f9d0dd5b63c8b3ac0767b4f65c892f56c10f":16:"010001":MBEDTLS_MD_NONE:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_RSA_SALT_LEN_ANY:"":"63a35294577c7e593170378175b7df27c293dae583ec2a971426eb2d66f2af483e897bfae5dc20300a9d61a3644e08c3aee61a463690a3498901563c46041056":MBEDTLS_ERR_RSA_INVALID_PADDING:MBEDTLS_ERR_RSA_INVALID_PADDING