diff --git a/src/spicy/spicyz/glue-compiler.cc b/src/spicy/spicyz/glue-compiler.cc
index 6c6120b377..a401d1f856 100644
--- a/src/spicy/spicyz/glue-compiler.cc
+++ b/src/spicy/spicyz/glue-compiler.cc
@@ -1165,7 +1165,7 @@ bool GlueCompiler::PopulateEvents() {
             // to a unit now.
             ev.unit = ev.path.namespace_();
             if ( ! ev.unit ) {
-                hilti::logger().error(hilti::util::fmt("unit type missing in hook '%s'", ev.path));
+                hilti::logger().error(hilti::util::fmt("namespace missing for '%s'", ev.path), ev.location);
                 return false;
             }
 
@@ -1174,7 +1174,7 @@ bool GlueCompiler::PopulateEvents() {
                 ev.hook = ev.path;
             }
             else {
-                hilti::logger().error(hilti::util::fmt("unknown unit type '%s'", ev.unit));
+                hilti::logger().error(hilti::util::fmt("no unit type of name '%s'", ev.path), ev.location);
                 return false;
             }
         }
diff --git a/testing/btest/Baseline/spicy.event-unit-type-fail-2/output b/testing/btest/Baseline/spicy.event-unit-type-fail-2/output
new file mode 100644
index 0000000000..7947117e1f
--- /dev/null
+++ b/testing/btest/Baseline/spicy.event-unit-type-fail-2/output
@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+[error] <...>/event-unit-type-fail.evt:5: no unit type of name 'TestAssertion::DoesNotExit'
+[error] <Spicy support for Zeek>: aborting after errors
diff --git a/testing/btest/Baseline/spicy.event-unit-type-fail-3/output b/testing/btest/Baseline/spicy.event-unit-type-fail-3/output
new file mode 100644
index 0000000000..07fecb2a5c
--- /dev/null
+++ b/testing/btest/Baseline/spicy.event-unit-type-fail-3/output
@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+[error] <...>/event-unit-type-fail.evt:5: no unit type of name 'TestAssertion::E'
+[error] <Spicy support for Zeek>: aborting after errors
diff --git a/testing/btest/Baseline/spicy.event-unit-type-fail/output b/testing/btest/Baseline/spicy.event-unit-type-fail/output
new file mode 100644
index 0000000000..5fa94c9936
--- /dev/null
+++ b/testing/btest/Baseline/spicy.event-unit-type-fail/output
@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+[error] <...>/event-unit-type-fail.evt:12: namespace missing for 'Data'
+[error] <Spicy support for Zeek>: aborting after errors
diff --git a/testing/btest/spicy/event-unit-type-fail.evt b/testing/btest/spicy/event-unit-type-fail.evt
new file mode 100644
index 0000000000..9f011046b5
--- /dev/null
+++ b/testing/btest/spicy/event-unit-type-fail.evt
@@ -0,0 +1,38 @@
+# @TEST-REQUIRES: have-spicy
+#
+# @TEST-EXEC-FAIL: spicyz -d -o test.hlto test.spicy %INPUT 2>output
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=diff-remove-abspath btest-diff output
+#
+# @TEST-DOC: Check that we catch various cases of invalid unit types in event definitions; regression test for #3988.
+
+protocol analyzer spicy::Test over TCP:
+    parse with TestAssertion::Data;
+
+on TestAssertion::Alias -> event Test::my_event(); # works
+on Data -> event Test::my_event(); # failure: can't find unit due to missing namespace
+
+@TEST-START-NEXT
+
+protocol analyzer spicy::Test over TCP:
+    parse with TestAssertion::Data;
+
+on TestAssertion::DoesNotExit -> event Test::my_event(); # failure: no such type
+
+@TEST-START-NEXT
+
+protocol analyzer spicy::Test over TCP:
+    parse with TestAssertion::Data;
+
+on TestAssertion::E -> event Test::my_event(); # failure: exists, but not a unit type
+
+@TEST-START-FILE test.spicy
+module TestAssertion;
+
+public type Data = unit {
+    : uint8;
+};
+
+public type Alias = Data;
+public type E = enum { One };
+@TEST-END-FILE
+