diff --git a/src/json-validator.cpp b/src/json-validator.cpp
index cd690cd..b82b19d 100644
--- a/src/json-validator.cpp
+++ b/src/json-validator.cpp
@@ -178,11 +178,13 @@ public:
 
 		// referencing an unknown keyword, turn it into schema
 		try {
-			auto &subschema = file.unknown_keywords.at(uri.pointer());
-			auto s = schema::make(subschema, this, {}, {{uri}});
-			file.unknown_keywords.erase(uri.fragment());
-			return s;
-		} catch (...) {
+			auto &subschema = file.unknown_keywords.at(uri.pointer()); // null is returned if not existing
+			auto s = schema::make(subschema, this, {}, {{uri}});       //  A JSON Schema MUST be an object or a boolean.
+			if (s) {                                                   // nullptr if invalid schema, e.g. null
+				file.unknown_keywords.erase(uri.fragment());
+				return s;
+			}
+		} catch (nlohmann::detail::out_of_range &) { // at() did not find it
 		}
 
 		// get or create a schema_ref
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 3371cb9..0de2a05 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -39,6 +39,10 @@ add_executable(issue-25-default-values issue-25-default-values.cpp)
 target_link_libraries(issue-25-default-values nlohmann_json_schema_validator)
 add_test(NAME issue-25-default-values COMMAND issue-25-default-values)
 
+add_executable(issue-98 issue-98.cpp)
+target_link_libraries(issue-98 nlohmann_json_schema_validator)
+add_test(NAME issue-98-erase-exception-unknown-keywords COMMAND issue-98)
+
 # Unit test for string format checks
 add_executable("string-format-check-test" "string-format-check-test.cpp")
 target_include_directories("string-format-check-test" PRIVATE "${PROJECT_SOURCE_DIR}/src/")
diff --git a/test/issue-98.cpp b/test/issue-98.cpp
new file mode 100644
index 0000000..7aafe47
--- /dev/null
+++ b/test/issue-98.cpp
@@ -0,0 +1,10 @@
+#include <nlohmann/json-schema.hpp>
+
+int main(void)
+{
+	nlohmann::json nlBase{{"$ref", "#/unknown/keywords"}};
+	nlohmann::json_schema::json_validator validator;
+	validator.set_root_schema(nlBase); // this line will log the caught exception
+
+	return 0;
+}