diff --git a/NEWS b/NEWS
index e2c2f7e7d45..c976a6b2c9d 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,10 @@ PHP                                                                        NEWS
 - PDO_MySQL:
   . Fixed bug #41997 (SP call yields additional empty result set). (cmb)
 
+- sodium:
+  . Fixed bug #78510 (Partially uninitialized buffer returned by
+    sodium_crypto_generichash_init()). (Frank Denis, cmb)
+
 05 Sep 2019, PHP 7.4.0RC1
 
 - Core:
diff --git a/ext/sodium/libsodium.c b/ext/sodium/libsodium.c
index 2159cb52b47..60bdd29aca0 100644
--- a/ext/sodium/libsodium.c
+++ b/ext/sodium/libsodium.c
@@ -952,6 +952,7 @@ PHP_FUNCTION(sodium_crypto_generichash_init)
 		zend_throw_exception(sodium_exception_ce, "unsupported key length", 0);
 		return;
 	}
+	memset(&state_tmp, 0, sizeof state_tmp);
 	if (crypto_generichash_init((void *) &state_tmp, key, (size_t) key_len,
 								(size_t) hash_len) != 0) {
 		zend_throw_exception(sodium_exception_ce, "internal error", 0);
diff --git a/ext/sodium/tests/bug78510.phpt b/ext/sodium/tests/bug78510.phpt
new file mode 100644
index 00000000000..dc7e4784249
--- /dev/null
+++ b/ext/sodium/tests/bug78510.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Bug #78510 (Partially uninitialized buffer returned by sodium_crypto_generichash_init())
+--SKIPIF--
+<?php
+if (!extension_loaded("sodium")) print "skip extension not loaded";
+?>
+--FILE--
+<?php
+$key = hex2bin('36be2998c85757e98c1abf3687c8db3a849a393701c05454023d9aba1096fd47');
+$y = sodium_crypto_generichash_init($key, 64);
+var_dump(bin2hex($y));
+?>
+--EXPECT--
+string(768) "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"