diff --git a/libcperciva/util/parsenum.h b/libcperciva/util/parsenum.h
index d8406c9b..3841361f 100644
--- a/libcperciva/util/parsenum.h
+++ b/libcperciva/util/parsenum.h
@@ -151,6 +151,8 @@ parsenum_float(const char * s, double min, double max, int trailing)
 	val = strtod(s, &eptr);
 	if (eptr == s || (!trailing && (*eptr != '\0')))
 		errno = EINVAL;
+	else if (isnan(val))
+		errno = EINVAL;
 	else if ((val < min) || (val > max))
 		errno = ERANGE;
 	return (val);
diff --git a/tests/09-explicit-params.sh b/tests/09-explicit-params.sh
index 7b75b05b..73c29239 100644
--- a/tests/09-explicit-params.sh
+++ b/tests/09-explicit-params.sh
@@ -63,4 +63,17 @@ scenario_cmd() {
 	    enc -p 12 "${reference_file}" 2>&1 |			\
 	    grep -q "If -p is set, --logN and -r must also be set"
 	echo $? > "${c_exitfile}"
+
+	# NaN is not a numeric value within any bounded resource range.
+	setup_check "scrypt rejects NaN maxmem fraction"
+	${c_valgrind_cmd} "${bindir}/scrypt" info -m NaN		\
+	    "${scriptdir}/verify-strings/test_scrypt_good.enc" 2>&1 |	\
+	    grep -q "Invalid option: -m NaN"
+	echo $? > "${c_exitfile}"
+
+	setup_check "scrypt rejects NaN max time"
+	${c_valgrind_cmd} "${bindir}/scrypt" info -t NaN		\
+	    "${scriptdir}/verify-strings/test_scrypt_good.enc" 2>&1 |	\
+	    grep -q "Invalid option: -t NaN"
+	echo $? > "${c_exitfile}"
 }