diff --git a/tests/src/fuzzer-parse_bjdata.cpp b/tests/src/fuzzer-parse_bjdata.cpp
index a88479933..41c51a311 100644
--- a/tests/src/fuzzer-parse_bjdata.cpp
+++ b/tests/src/fuzzer-parse_bjdata.cpp
@@ -46,10 +46,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // value-stable comparison for the round-trip checks below; see the note
diff --git a/tests/src/fuzzer-parse_bson.cpp b/tests/src/fuzzer-parse_bson.cpp
index c5f74c7cc..16f36445b 100644
--- a/tests/src/fuzzer-parse_bson.cpp
+++ b/tests/src/fuzzer-parse_bson.cpp
@@ -19,10 +19,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // see http://llvm.org/docs/LibFuzzer.html
diff --git a/tests/src/fuzzer-parse_cbor.cpp b/tests/src/fuzzer-parse_cbor.cpp
index b38e3c1e5..7d599abe2 100644
--- a/tests/src/fuzzer-parse_cbor.cpp
+++ b/tests/src/fuzzer-parse_cbor.cpp
@@ -19,10 +19,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // see http://llvm.org/docs/LibFuzzer.html
diff --git a/tests/src/fuzzer-parse_json.cpp b/tests/src/fuzzer-parse_json.cpp
index 59a278c7b..217d9e0fd 100644
--- a/tests/src/fuzzer-parse_json.cpp
+++ b/tests/src/fuzzer-parse_json.cpp
@@ -20,10 +20,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // see http://llvm.org/docs/LibFuzzer.html
diff --git a/tests/src/fuzzer-parse_msgpack.cpp b/tests/src/fuzzer-parse_msgpack.cpp
index 0b4ab0af7..df961b8d7 100644
--- a/tests/src/fuzzer-parse_msgpack.cpp
+++ b/tests/src/fuzzer-parse_msgpack.cpp
@@ -19,10 +19,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // see http://llvm.org/docs/LibFuzzer.html
diff --git a/tests/src/fuzzer-parse_ubjson.cpp b/tests/src/fuzzer-parse_ubjson.cpp
index 463656c71..20c20eda7 100644
--- a/tests/src/fuzzer-parse_ubjson.cpp
+++ b/tests/src/fuzzer-parse_ubjson.cpp
@@ -25,10 +25,16 @@ The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
+#include <cassert>
 #include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 
+// the round-trip checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
 using json = nlohmann::json;
 
 // see http://llvm.org/docs/LibFuzzer.html