diff --git a/src/base64.c b/src/base64.c
index a5fedc86..ab6077fd 100644
--- a/src/base64.c
+++ b/src/base64.c
@@ -118,10 +118,6 @@ static size_t li_base64_decode(unsigned char * const result, const size_t out_le
 }
 
 size_t li_to_base64_no_padding(char* out, size_t out_length, const unsigned char* in, size_t in_length, base64_charset charset) {
-	const size_t full_tuples = in_length / 3;
-	const size_t in_tuple_remainder = in_length % 3;
-	const size_t out_tuple_remainder = in_tuple_remainder ? 1 + in_tuple_remainder : 0;
-	const size_t require_space = 4 * full_tuples + out_tuple_remainder;
 	size_t i;
 	size_t out_pos = 0;
 	const char* const base64_table = (charset)
@@ -131,10 +127,8 @@ size_t li_to_base64_no_padding(char* out, size_t out_length, const unsigned char
 	/* check overflows */
 	/* 1073741823 is max num full_tuples to avoid overflow in uint32_t;
 	 * and (1 GB - 1) is ridiculously large for base64-encoded data */
-	force_assert(full_tuples <= 1073741823);
-	/*force_assert(full_tuples <= 4*full_tuples);*/
-	/*force_assert(4*full_tuples <= 4*full_tuples + out_tuple_remainder);*/
-	force_assert(require_space <= out_length);
+	force_assert(in_length <= 3221225469); /* (3221225469+2) / 3 * 4 < UINT32_MAX */
+	force_assert((in_length+2)/3*4 <= out_length);
 
 	for (i = 2; i < in_length; i += 3) {
 		unsigned int v = (in[i-2] << 16) | (in[i-1] << 8) | in[i];
@@ -144,8 +138,10 @@ size_t li_to_base64_no_padding(char* out, size_t out_length, const unsigned char
 		out[out_pos+0] = base64_table[v & 0x3f];
 		out_pos += 4;
 	}
-	switch (in_tuple_remainder) {
+
+	switch (in_length - (i-2)) {
 	case 0:
+	default:
 		break;
 	case 1:
 		{
@@ -167,7 +163,6 @@ size_t li_to_base64_no_padding(char* out, size_t out_length, const unsigned char
 		}
 		break;
 	}
-	force_assert(out_pos <= out_length);
 	return out_pos;
 }
 
@@ -190,7 +185,7 @@ size_t li_to_base64(char* out, size_t out_length, const unsigned char* in, size_
 
 
 char* buffer_append_base64_encode_opt(buffer *out, const unsigned char* in, size_t in_length, base64_charset charset, int pad) {
-    const size_t reserve = 4*(in_length/3) + 4;
+    const size_t reserve = (in_length+2)/3*4;
     char * const result = buffer_string_prepare_append(out, reserve);
     const size_t out_pos = (pad)
       ? li_to_base64(result, reserve, in, in_length, charset)
diff --git a/src/mod_secdownload.c b/src/mod_secdownload.c
index ea6a8e74..885cc32b 100644
--- a/src/mod_secdownload.c
+++ b/src/mod_secdownload.c
@@ -166,7 +166,7 @@ static int secdl_verify_mac(plugin_config *config, const char* protected_path, c
 	case SECDL_HMAC_SHA1:
 		{
 			unsigned char digest[20];
-			char base64_digest[27];
+			char base64_digest[28];
 
                         if (!li_hmac_sha1(digest, CONST_BUF_LEN(config->secret),
 			                  (const unsigned char *)protected_path,
@@ -176,7 +176,7 @@ static int secdl_verify_mac(plugin_config *config, const char* protected_path, c
 				return 0;
 			}
 
-			li_to_base64_no_padding(base64_digest, 27, digest, 20, BASE64_URL);
+			li_to_base64_no_padding(base64_digest, 28, digest, 20, BASE64_URL);
 
 			return (27 == maclen)
 			    && http_auth_const_time_memeq(mac, base64_digest, 27);
@@ -185,7 +185,7 @@ static int secdl_verify_mac(plugin_config *config, const char* protected_path, c
 	case SECDL_HMAC_SHA256:
 		{
 			unsigned char digest[32];
-			char base64_digest[43];
+			char base64_digest[44];
 
                         if (!li_hmac_sha256(digest, CONST_BUF_LEN(config->secret),
 			                    (const unsigned char *)protected_path,
@@ -195,7 +195,7 @@ static int secdl_verify_mac(plugin_config *config, const char* protected_path, c
 				return 0;
 			}
 
-			li_to_base64_no_padding(base64_digest, 43, digest, 32, BASE64_URL);
+			li_to_base64_no_padding(base64_digest, 44, digest, 32, BASE64_URL);
 
 			return (43 == maclen)
 			    && http_auth_const_time_memeq(mac, base64_digest, 43);
diff --git a/src/t/test_base64.c b/src/t/test_base64.c
index be0a70e0..fd188fc5 100644
--- a/src/t/test_base64.c
+++ b/src/t/test_base64.c
@@ -6,24 +6,24 @@ static const base64_charset encs[] = { BASE64_STANDARD, BASE64_URL };
 static buffer *check;
 
 inline
-static void check_base64 (char *out, const size_t out_sz, const char *in, const size_t in_len, const base64_charset enc) {
-	force_assert(out_sz == li_to_base64_no_padding(out, out_sz, (const unsigned char *)in, in_len, enc));
+static void check_base64 (size_t out_exp, const char *in, const size_t in_len, const base64_charset enc) {
+	char out[4] = { 0, 0, 0, 0 };
+	force_assert(out_exp == li_to_base64_no_padding(out, sizeof(out), (const unsigned char *)in, in_len, enc));
 
 	buffer_clear(check);
-	force_assert(NULL != buffer_append_base64_decode(check, out, out_sz, enc));
+	force_assert(NULL != buffer_append_base64_decode(check, out, out_exp, enc));
 	force_assert(buffer_eq_slen(check, in, in_len));
 }
 
 static void check_all_len_0 (const base64_charset enc) {
-	check_base64(NULL, 0, "", 0, enc);
+	check_base64(0, "", 0, enc);
 }
 
 static void check_all_len_1 (const base64_charset enc) {
 	unsigned int c1;
 	for (c1 = 0; c1 < 256; ++c1) {
 			unsigned char in[] = { c1 };
-			char out[2] = { 0, 0 };
-			check_base64(out, sizeof(out), (char *)in, sizeof(in), enc);
+			check_base64(2, (char *)in, sizeof(in), enc);
 	}
 }
 
@@ -31,8 +31,7 @@ static void check_all_len_2 (const base64_charset enc) {
 	unsigned int c1, c2;
 	for (c1 = 0; c1 < 256; ++c1) for (c2 = 0; c2 < 256; ++c2) {
 			unsigned char in[] = { c1, c2 };
-			char out[3] = { 0, 0, 0 };
-			check_base64(out, sizeof(out), (char *)in, sizeof(in), enc);
+			check_base64(3, (char *)in, sizeof(in), enc);
 	}
 }
 
@@ -40,8 +39,7 @@ static void check_all_len_3 (const base64_charset enc) {
 	unsigned int c1, c2, c3;
 	for (c1 = 0; c1 < 256; c1+=255) for (c2 = 0; c2 < 256; ++c2) for (c3 = 0; c3 < 256; ++c3) {
 			unsigned char in[] = { c1, c2, c3 };
-			char out[4] = { 0, 0, 0, 0 };
-			check_base64(out, sizeof(out), (char *)in, sizeof(in), enc);
+			check_base64(4, (char *)in, sizeof(in), enc);
 	}
 }