diff --git a/CHANGES b/CHANGES
index 0359b0169e..eb92c339dd 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+3898.	[bug]		To small a buffer in tohexstr() calls in test code.
+			[RT #36598]
+
 3897.	[bug]		RPZ summary information was not properly being updated
 			after a AXFR resulting in changes sometimes being
 			ignored.  [RT #35885]
diff --git a/lib/dns/tests/gost_test.c b/lib/dns/tests/gost_test.c
index b254f60462..d04d44552f 100644
--- a/lib/dns/tests/gost_test.c
+++ b/lib/dns/tests/gost_test.c
@@ -54,7 +54,7 @@
 unsigned char digest[ISC_GOST_DIGESTLENGTH];
 unsigned char buffer[1024];
 const char *s;
-char str[ISC_GOST_DIGESTLENGTH];
+char str[2 * ISC_GOST_DIGESTLENGTH + 1];
 int i = 0;
 
 isc_result_t
@@ -65,7 +65,7 @@ tohexstr(unsigned char *d, unsigned int len, char *out);
  * Postcondition: A String representation of the given hexadecimal number is
  *   placed into the array *out
  *
- * 'out' MUST point to an array of at least len / 2 + 1
+ * 'out' MUST point to an array of at least len * 2 + 1
  *
  * Return values: ISC_R_SUCCESS if the operation is sucessful
  */
diff --git a/lib/isc/tests/hash_test.c b/lib/isc/tests/hash_test.c
index 5f937db03d..407eff6a1b 100644
--- a/lib/isc/tests/hash_test.c
+++ b/lib/isc/tests/hash_test.c
@@ -40,7 +40,7 @@
 unsigned char digest[ISC_SHA512_DIGESTLENGTH];
 unsigned char buffer[1024];
 const char *s;
-char str[ISC_SHA512_DIGESTLENGTH];
+char str[2 * ISC_SHA512_DIGESTLENGTH + 1];
 unsigned char key[20];
 int i = 0;
 
@@ -52,7 +52,7 @@ tohexstr(unsigned char *d, unsigned int len, char *out);
  * Postcondition: A String representation of the given hexadecimal number is
  *   placed into the array *out
  *
- * 'out' MUST point to an array of at least len / 2 + 1
+ * 'out' MUST point to an array of at least len * 2 + 1
  *
  * Return values: ISC_R_SUCCESS if the operation is sucessful
  */