diff --git a/test/openpower-pels/ascii_string_test.cpp b/test/openpower-pels/ascii_string_test.cpp
index 96ee4ad..2d23847 100644
--- a/test/openpower-pels/ascii_string_test.cpp
+++ b/test/openpower-pels/ascii_string_test.cpp
@@ -84,3 +84,16 @@
 
     EXPECT_THROW(src::AsciiString as{stream}, std::out_of_range);
 }
+
+TEST(AsciiStringTest, MissingSubsystemTest)
+{
+    message::Entry entry;
+    entry.src.type = 0xBD;
+    entry.src.reasonCode = 0xABCD;
+
+    src::AsciiString as{entry};
+    auto data = as.get();
+
+    // Default subsystem is 0x70
+    EXPECT_EQ(data, "BD70ABCD                        ");
+}
diff --git a/test/openpower-pels/registry_test.cpp b/test/openpower-pels/registry_test.cpp
index c7d88c9..5cfd5e5 100644
--- a/test/openpower-pels/registry_test.cpp
+++ b/test/openpower-pels/registry_test.cpp
@@ -101,6 +101,21 @@
                     "dump that provides debug information."
                 ]
             }
+        },
+
+        {
+            "Name": "xyz.openbmc_project.Common.Error.Timeout",
+            "PossibleSubsystems": ["processor", "memory"],
+
+            "SRC":
+            {
+                "ReasonCode": "0x2030"
+            },
+            "Documentation":
+            {
+                "Description": "A PGOOD Fault",
+                "Message": "PS had a PGOOD Fault"
+            }
         }
     ]
 }
@@ -651,3 +666,14 @@
         }
     }
 }
+
+TEST_F(RegistryTest, TestNoSubsystem)
+{
+    auto path = RegistryTest::writeData(registryData);
+    Registry registry{path};
+
+    auto entry = registry.lookup("xyz.openbmc_project.Common.Error.Timeout",
+                                 LookupType::name);
+    ASSERT_TRUE(entry);
+    EXPECT_FALSE(entry->subsystem);
+}
diff --git a/test/openpower-pels/user_header_test.cpp b/test/openpower-pels/user_header_test.cpp
index 59199fb..233f08b 100644
--- a/test/openpower-pels/user_header_test.cpp
+++ b/test/openpower-pels/user_header_test.cpp
@@ -313,19 +313,56 @@
 TEST(UserHeaderTest, UseEventLogPELSubsystem)
 {
     using namespace openpower::pels::message;
-    Entry regEntry;
 
-    regEntry.name = "test";
-    regEntry.subsystem = 5;
-    regEntry.actionFlags = 0xC000;
-    regEntry.eventType = 1;
-    regEntry.eventScope = 2;
+    {
+        Entry regEntry;
 
-    MockDataInterface dataIface;
-    std::vector<std::string> adData{"PEL_SUBSYSTEM=0x25"};
-    AdditionalData ad{adData};
+        regEntry.name = "test";
+        regEntry.subsystem = 5;
+        regEntry.actionFlags = 0xC000;
+        regEntry.eventType = 1;
+        regEntry.eventScope = 2;
 
-    UserHeader uh(regEntry, phosphor::logging::Entry::Level::Critical, ad,
-                  dataIface);
-    ASSERT_EQ(uh.subsystem(), 0x25);
+        MockDataInterface dataIface;
+        std::vector<std::string> adData{"PEL_SUBSYSTEM=0x25"};
+        AdditionalData ad{adData};
+
+        UserHeader uh(regEntry, phosphor::logging::Entry::Level::Critical, ad,
+                      dataIface);
+        ASSERT_EQ(uh.subsystem(), 0x25);
+    }
+    {
+        // No subsystem in registry, and invalid PEL_SUBSYSTEM
+        Entry regEntry;
+
+        regEntry.name = "test";
+        regEntry.actionFlags = 0xC000;
+        regEntry.eventType = 1;
+        regEntry.eventScope = 2;
+
+        MockDataInterface dataIface;
+        std::vector<std::string> adData{"PEL_SUBSYSTEM=0x99"};
+        AdditionalData ad{adData};
+
+        UserHeader uh(regEntry, phosphor::logging::Entry::Level::Critical, ad,
+                      dataIface);
+        ASSERT_EQ(uh.subsystem(), 0x70); // others
+    }
+    {
+        // No subsystem in registry or PEL_SUBSYSTEM
+        Entry regEntry;
+
+        regEntry.name = "test";
+        regEntry.actionFlags = 0xC000;
+        regEntry.eventType = 1;
+        regEntry.eventScope = 2;
+
+        MockDataInterface dataIface;
+        std::vector<std::string> adData;
+        AdditionalData ad{adData};
+
+        UserHeader uh(regEntry, phosphor::logging::Entry::Level::Critical, ad,
+                      dataIface);
+        ASSERT_EQ(uh.subsystem(), 0x70); // others
+    }
 }