diff --git a/extensions/openpower-pels/json_utils.hpp b/extensions/openpower-pels/json_utils.hpp
index f6db297..6415c9e 100644
--- a/extensions/openpower-pels/json_utils.hpp
+++ b/extensions/openpower-pels/json_utils.hpp
@@ -71,10 +71,15 @@
     static_assert(std::is_integral<T>::value, "Integral required.");
 
     int len = asprintf(&value, format, number);
-    if (len)
+    if (len >= 0)
     {
         numString = value;
     }
+    else
+    {
+        throw std::invalid_argument(
+            std::string("getNumberString: invalid format string: ") + format);
+    }
     free(value);
 
     return numString;
diff --git a/test/openpower-pels/json_utils_test.cpp b/test/openpower-pels/json_utils_test.cpp
index 60ca00d..a7203aa 100644
--- a/test/openpower-pels/json_utils_test.cpp
+++ b/test/openpower-pels/json_utils_test.cpp
@@ -35,8 +35,7 @@
     EXPECT_EQ(getNumberString("%d", number), "123");
     EXPECT_EQ(getNumberString("%03X", number), "07B");
     EXPECT_EQ(getNumberString("0x%X", number), "0x7B");
-    ASSERT_EXIT((getNumberString("%123", number), exit(0)),
-                ::testing::KilledBySignal(SIGSEGV), ".*");
+    EXPECT_THROW(getNumberString("%123", number), std::invalid_argument);
 }
 
 TEST(JsonUtilsTest, JsonInsertTest)