diff --git a/ChangeLog b/ChangeLog
index def9703..7ac65ee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,8 @@
      was independently reported by Tim Nordell via e-mail and by Florin Petriuc
      and sjorsdewit on GitHub. Fix proposed by Florin Petriuc in #1022. Fixes #707.
    * Tighten should-be-constant-time memcmp against compiler optimizations.
+   * Ensure that buffers are cleared after use if they contain sensitive data.
+     Changes were introduced in multiple places in the library.
 
 Features
    * Allow comments in test data files.
diff --git a/library/bignum.c b/library/bignum.c
index d3a150c..bd8280b 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -63,6 +63,10 @@
     volatile mbedtls_mpi_uint *p = v; while( n-- ) *p++ = 0;
 }
 
+static void mbedtls_zeroize( void *v, size_t n ) {
+    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
+}
+
 #define ciL    (sizeof(mbedtls_mpi_uint))         /* chars in limb  */
 #define biL    (ciL << 3)               /* bits  in limb  */
 #define biH    (ciL << 2)               /* half limb size */
@@ -1882,6 +1886,8 @@
     MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( X, buf, size ) );
 
 cleanup:
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
     return( ret );
 }
 
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 55612c7..a31f7b8 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -430,20 +430,20 @@
         goto exit;
 
     if( fwrite( buf, 1, MBEDTLS_CTR_DRBG_MAX_INPUT, f ) != MBEDTLS_CTR_DRBG_MAX_INPUT )
-    {
         ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
-        goto exit;
-    }
-
-    ret = 0;
+    else
+        ret = 0;
 
 exit:
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
     fclose( f );
     return( ret );
 }
 
 int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path )
 {
+    int ret = 0;
     FILE *f;
     size_t n;
     unsigned char buf[ MBEDTLS_CTR_DRBG_MAX_INPUT ];
@@ -462,14 +462,16 @@
     }
 
     if( fread( buf, 1, n, f ) != n )
-    {
-        fclose( f );
-        return( MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR );
-    }
+        ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
+    else
+        mbedtls_ctr_drbg_update( ctx, buf, n );
 
     fclose( f );
 
-    mbedtls_ctr_drbg_update( ctx, buf, n );
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
+    if( ret != 0 )
+        return( ret );
 
     return( mbedtls_ctr_drbg_write_seed_file( ctx, path ) );
 }
diff --git a/library/dhm.c b/library/dhm.c
index bec52a1..7076e68 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -542,7 +542,10 @@
     if( fread( *buf, 1, *n, f ) != *n )
     {
         fclose( f );
+
+        mbedtls_zeroize( *buf, *n + 1 );
         mbedtls_free( *buf );
+
         return( MBEDTLS_ERR_DHM_FILE_IO_ERROR );
     }
 
diff --git a/library/entropy.c b/library/entropy.c
index 23de406..d878ca6 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -195,6 +195,8 @@
     mbedtls_sha256_update( &ctx->accumulator, p, use_len );
 #endif
 
+    mbedtls_zeroize( tmp, sizeof( tmp ) );
+
     return( 0 );
 }
 
@@ -242,7 +244,7 @@
         if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
                         buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen ) ) != 0 )
         {
-            return( ret );
+            goto cleanup;
         }
 
         /*
@@ -256,9 +258,12 @@
     }
 
     if( have_one_strong == 0 )
-        return( MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE );
+        ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;
 
-    return( 0 );
+cleanup:
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
+    return( ret );
 }
 
 /*
@@ -370,6 +375,8 @@
     ret = 0;
 
 exit:
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
@@ -382,7 +389,7 @@
 int mbedtls_entropy_update_nv_seed( mbedtls_entropy_context *ctx )
 {
     int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
-    unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
 
     /* Read new seed  and write it to NV */
     if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
@@ -393,9 +400,9 @@
 
     /* Manually update the remaining stream with a separator value to diverge */
     memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
-    mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
+    ret = mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
 
-    return( 0 );
+    return( ret );
 }
 #endif /* MBEDTLS_ENTROPY_NV_SEED */
 
@@ -421,12 +428,15 @@
     ret = 0;
 
 exit:
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
     fclose( f );
     return( ret );
 }
 
 int mbedtls_entropy_update_seed_file( mbedtls_entropy_context *ctx, const char *path )
 {
+    int ret = 0;
     FILE *f;
     size_t n;
     unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];
@@ -442,14 +452,16 @@
         n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;
 
     if( fread( buf, 1, n, f ) != n )
-    {
-        fclose( f );
-        return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
-    }
+        ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
+    else
+        ret = mbedtls_entropy_update_manual( ctx, buf, n );
 
     fclose( f );
 
-    mbedtls_entropy_update_manual( ctx, buf, n );
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
+    if( ret != 0 )
+        return( ret );
 
     return( mbedtls_entropy_write_seed_file( ctx, path ) );
 }
diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index bf5f9b5..24c609e 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -364,11 +364,14 @@
 
 exit:
     fclose( f );
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
     return( ret );
 }
 
 int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path )
 {
+    int ret = 0;
     FILE *f;
     size_t n;
     unsigned char buf[ MBEDTLS_HMAC_DRBG_MAX_INPUT ];
@@ -387,14 +390,16 @@
     }
 
     if( fread( buf, 1, n, f ) != n )
-    {
-        fclose( f );
-        return( MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR );
-    }
+        ret = MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR;
+    else
+        mbedtls_hmac_drbg_update( ctx, buf, n );
 
     fclose( f );
 
-    mbedtls_hmac_drbg_update( ctx, buf, n );
+    mbedtls_zeroize( buf, sizeof( buf ) );
+
+    if( ret != 0 )
+        return( ret );
 
     return( mbedtls_hmac_drbg_write_seed_file( ctx, path ) );
 }
diff --git a/library/md.c b/library/md.c
index eda98f6..75b9717 100644
--- a/library/md.c
+++ b/library/md.c
@@ -312,12 +312,11 @@
         md_info->update_func( ctx.md_ctx, buf, n );
 
     if( ferror( f ) != 0 )
-    {
         ret = MBEDTLS_ERR_MD_FILE_IO_ERROR;
-        goto cleanup;
-    }
+    else
+        md_info->finish_func( ctx.md_ctx, output );
 
-    md_info->finish_func( ctx.md_ctx, output );
+    mbedtls_zeroize( buf, sizeof( buf ) );
 
 cleanup:
     fclose( f );
diff --git a/library/pem.c b/library/pem.c
index 8dd86a4..ea36df8 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -331,6 +331,7 @@
 
     if( ( ret = mbedtls_base64_decode( buf, len, &len, s1, s2 - s1 ) ) != 0 )
     {
+        mbedtls_zeroize( buf, len );
         mbedtls_free( buf );
         return( MBEDTLS_ERR_PEM_INVALID_DATA + ret );
     }
@@ -341,6 +342,7 @@
     ( defined(MBEDTLS_DES_C) || defined(MBEDTLS_AES_C) )
         if( pwd == NULL )
         {
+            mbedtls_zeroize( buf, len );
             mbedtls_free( buf );
             return( MBEDTLS_ERR_PEM_PASSWORD_REQUIRED );
         }
@@ -369,10 +371,12 @@
          */
         if( len <= 2 || buf[0] != 0x30 || buf[1] > 0x83 )
         {
+            mbedtls_zeroize( buf, len );
             mbedtls_free( buf );
             return( MBEDTLS_ERR_PEM_PASSWORD_MISMATCH );
         }
 #else
+        mbedtls_zeroize( buf, len );
         mbedtls_free( buf );
         return( MBEDTLS_ERR_PEM_FEATURE_UNAVAILABLE );
 #endif /* MBEDTLS_MD5_C && MBEDTLS_CIPHER_MODE_CBC &&
diff --git a/library/pkparse.c b/library/pkparse.c
index 968c83f..eec6127 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -101,7 +101,10 @@
     if( fread( *buf, 1, *n, f ) != *n )
     {
         fclose( f );
+
+        mbedtls_zeroize( *buf, *n );
         mbedtls_free( *buf );
+
         return( MBEDTLS_ERR_PK_FILE_IO_ERROR );
     }
 
diff --git a/library/platform.c b/library/platform.c
index af3b2f1..b882b65 100644
--- a/library/platform.c
+++ b/library/platform.c
@@ -228,12 +228,13 @@
     size_t n;
 
     if( ( file = fopen( MBEDTLS_PLATFORM_STD_NV_SEED_FILE, "rb" ) ) == NULL )
-        return -1;
+        return( -1 );
 
     if( ( n = fread( buf, 1, buf_len, file ) ) != buf_len )
     {
         fclose( file );
-        return -1;
+        mbedtls_zeroize( buf, buf_len );
+        return( -1 );
     }
 
     fclose( file );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index e19dfc9..33ad722 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6056,12 +6056,19 @@
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
     }
 
-    if( conf->psk != NULL || conf->psk_identity != NULL )
+    if( conf->psk != NULL )
     {
+        mbedtls_zeroize( conf->psk, conf->psk_len );
+
         mbedtls_free( conf->psk );
-        mbedtls_free( conf->psk_identity );
         conf->psk = NULL;
+        conf->psk_len = 0;
+    }
+    if( conf->psk_identity != NULL )
+    {
+        mbedtls_free( conf->psk_identity );
         conf->psk_identity = NULL;
+        conf->psk_identity_len = 0;
     }
 
     if( ( conf->psk = mbedtls_calloc( 1, psk_len ) ) == NULL ||
@@ -6093,7 +6100,11 @@
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
 
     if( ssl->handshake->psk != NULL )
+    {
+        mbedtls_zeroize( ssl->handshake->psk, ssl->handshake->psk_len );
         mbedtls_free( ssl->handshake->psk );
+        ssl->handshake->psk_len = 0;
+    }
 
     if( ( ssl->handshake->psk = mbedtls_calloc( 1, psk_len ) ) == NULL )
         return( MBEDTLS_ERR_SSL_ALLOC_FAILED );