diff --git a/ChangeLog.d/chacha20_invalid_iv_len_fix.txt b/ChangeLog.d/chacha20_invalid_iv_len_fix.txt
new file mode 100644
index 0000000..af35e2a
--- /dev/null
+++ b/ChangeLog.d/chacha20_invalid_iv_len_fix.txt
@@ -0,0 +1,4 @@
+Default behavior changes
+   * mbedtls_cipher_set_iv will now fail with ChaCha20 and ChaCha20+Poly1305
+     for IV lengths other than 12. The library was silently overwriting this
+     length with 12, but did not inform the caller about it. Fixes #4301.
diff --git a/library/cipher.c b/library/cipher.c
index 4ec40d2..f3b4bd2 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -386,6 +386,12 @@
 #if defined(MBEDTLS_CHACHA20_C)
     if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
     {
+        /* Even though the actual_iv_size is overwritten with a correct value
+         * of 12 from the cipher info, return an error to indicate that
+         * the input iv_len is wrong. */
+        if( iv_len != 12 )
+            return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
         if ( 0 != mbedtls_chacha20_starts( (mbedtls_chacha20_context*)ctx->cipher_ctx,
                                            iv,
                                            0U ) ) /* Initial counter value */
@@ -393,6 +399,11 @@
             return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
         }
     }
+#if defined(MBEDTLS_CHACHAPOLY_C)
+    if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 &&
+         iv_len != 12 )
+        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+#endif
 #endif
 
     if ( actual_iv_size != 0 )
diff --git a/tests/suites/test_suite_cipher.chacha20.data b/tests/suites/test_suite_cipher.chacha20.data
index 11de103..dfa0e76 100644
--- a/tests/suites/test_suite_cipher.chacha20.data
+++ b/tests/suites/test_suite_cipher.chacha20.data
@@ -1,3 +1,7 @@
+Decrypt empty buffer
+depends_on:MBEDTLS_CHACHAPOLY_C
+dec_empty_buf:MBEDTLS_CIPHER_CHACHA20:0:0
+
 Chacha20 RFC 7539 Test Vector #1
 depends_on:MBEDTLS_CHACHA20_C
 decrypt_test_vec:MBEDTLS_CIPHER_CHACHA20:-1:"0000000000000000000000000000000000000000000000000000000000000000":"000000000000000000000000":"76b8e0ada0f13d90405d6ae55386bd28bdd219b8a08ded1aa836efcc8b770dc7da41597c5157488d7724e03fb8d84a376a43b8f41518a11cc387b669b2ee6586":"00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000":"":"":0:0
@@ -109,3 +113,23 @@
 ChaCha20 Encrypt and decrypt 32 bytes in multiple parts
 depends_on:MBEDTLS_CHACHA20_C
 enc_dec_buf_multipart:MBEDTLS_CIPHER_CHACHA20:256:16:16:-1:16:16:16:16
+
+ChaCha20 IV Length 0
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":0:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 11
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":11:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 12
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":12:0
+
+ChaCha20 IV Length 13
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":13:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 16
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":16:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
diff --git a/tests/suites/test_suite_cipher.chachapoly.data b/tests/suites/test_suite_cipher.chachapoly.data
index 8c246ad..908951a 100644
--- a/tests/suites/test_suite_cipher.chachapoly.data
+++ b/tests/suites/test_suite_cipher.chachapoly.data
@@ -121,3 +121,23 @@
 Chacha20+Poly1305 RFC 7539 Test Vector #1 (streaming)
 depends_on:MBEDTLS_CHACHAPOLY_C
 decrypt_test_vec:MBEDTLS_CIPHER_CHACHA20_POLY1305:-1:"1c9240a5eb55d38af333888604f6b5f0473917c1402b80099dca5cbc207075c0":"000000000102030405060708":"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":"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":"f33388860000000000004e91":"eead9d67890cbb22392336fea1851f38":0:0
+
+ChaCha20+Poly1305 IV Length 0
+depends_on:MBEDTLS_CHACHAPOLY_C
+check_iv:MBEDTLS_CIPHER_CHACHA20_POLY1305:"CHACHA20-POLY1305":0:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20+Poly1305 IV Length 11
+depends_on:MBEDTLS_CHACHAPOLY_C
+check_iv:MBEDTLS_CIPHER_CHACHA20_POLY1305:"CHACHA20-POLY1305":11:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20+Poly1305 IV Length 12
+depends_on:MBEDTLS_CHACHAPOLY_C
+check_iv:MBEDTLS_CIPHER_CHACHA20_POLY1305:"CHACHA20-POLY1305":12:0
+
+ChaCha20+Poly1305 IV Length 13
+depends_on:MBEDTLS_CHACHAPOLY_C
+check_iv:MBEDTLS_CIPHER_CHACHA20_POLY1305:"CHACHA20-POLY1305":13:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20+Poly1305 IV Length 16
+depends_on:MBEDTLS_CHACHAPOLY_C
+check_iv:MBEDTLS_CIPHER_CHACHA20_POLY1305:"CHACHA20-POLY1305":16:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index b0b1629..03c1733 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -703,7 +703,7 @@
 void enc_dec_buf( int cipher_id, char * cipher_string, int key_len,
                   int length_val, int pad_mode )
 {
-    size_t length = length_val, outlen, total_len, i, block_size;
+    size_t length = length_val, outlen, total_len, i, block_size, iv_len;
     unsigned char key[64];
     unsigned char iv[16];
     unsigned char ad[13];
@@ -759,8 +759,14 @@
     memset( decbuf, 0, sizeof( decbuf ) );
     memset( tag, 0, sizeof( tag ) );
 
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, sizeof( iv ) ) );
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, sizeof( iv ) ) );
+    if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 ||
+        cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 )
+        iv_len = 12;
+    else
+        iv_len = sizeof(iv);
+
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
 
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_dec ) );
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_enc ) );
@@ -883,6 +889,7 @@
 {
     unsigned char key[32];
     unsigned char iv[16];
+    size_t iv_len = sizeof(iv);
 
     mbedtls_cipher_context_t ctx_dec;
     const mbedtls_cipher_info_t *cipher_info;
@@ -903,6 +910,11 @@
     /* Initialise context */
     cipher_info = mbedtls_cipher_info_from_type( cipher );
     TEST_ASSERT( NULL != cipher_info);
+
+    if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 ||
+        cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 )
+        iv_len = 12;
+
     TEST_ASSERT( sizeof(key) * 8 >= cipher_info->key_bitlen );
 
     TEST_ASSERT( 0 == mbedtls_cipher_setup( &ctx_dec, cipher_info ) );
@@ -911,7 +923,7 @@
                                              key, cipher_info->key_bitlen,
                                              MBEDTLS_DECRYPT ) );
 
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, 16 ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
 
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_dec ) );
 
@@ -954,7 +966,7 @@
     size_t first_length = first_length_val;
     size_t second_length = second_length_val;
     size_t length = first_length + second_length;
-    size_t block_size;
+    size_t block_size, iv_len;
     unsigned char key[32];
     unsigned char iv[16];
 
@@ -999,8 +1011,14 @@
     (void) pad_mode;
 #endif /* MBEDTLS_CIPHER_MODE_WITH_PADDING */
 
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, 16 ) );
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, 16 ) );
+    if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 ||
+        cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 )
+        iv_len = 12;
+    else
+        iv_len = sizeof(iv);
+
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
 
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_dec ) );
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_enc ) );
@@ -1579,3 +1597,38 @@
         TEST_ASSERT( dlen == (size_t) dlen_check );
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void check_iv( int cipher_id, char * cipher_string,
+               int iv_len_val, int ret )
+{
+    size_t iv_len = iv_len_val;
+    unsigned char iv[16];
+
+    const mbedtls_cipher_info_t *cipher_info;
+    mbedtls_cipher_context_t ctx_dec;
+    mbedtls_cipher_context_t ctx_enc;
+
+    /*
+     * Prepare contexts
+     */
+    mbedtls_cipher_init( &ctx_dec );
+    mbedtls_cipher_init( &ctx_enc );
+
+    /* Check and get info structures */
+    cipher_info = mbedtls_cipher_info_from_type( cipher_id );
+    TEST_ASSERT( NULL != cipher_info );
+    TEST_ASSERT( mbedtls_cipher_info_from_string( cipher_string ) == cipher_info );
+
+    /* Initialise enc and dec contexts */
+    TEST_ASSERT( 0 == mbedtls_cipher_setup( &ctx_dec, cipher_info ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_setup( &ctx_enc, cipher_info ) );
+
+    TEST_ASSERT( ret == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( ret == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
+
+exit:
+    mbedtls_cipher_free( &ctx_dec );
+    mbedtls_cipher_free( &ctx_enc );
+}
+/* END_CASE */