diff --git a/autotest/gcore/misc.py b/autotest/gcore/misc.py
index 18d1f4c806c0..62f8b29a5663 100755
--- a/autotest/gcore/misc.py
+++ b/autotest/gcore/misc.py
@@ -13,6 +13,7 @@
 # SPDX-License-Identifier: MIT
 ###############################################################################
 
+import datetime
 import os
 import shutil
 
@@ -721,6 +722,70 @@ def test_misc_13():
     assert out_ds is None
 
 
+###############################################################################
+# Test parsing of CPL_DEBUG and CPL_TIMESTAMP
+
+
+@pytest.fixture
+def debug_output():
+
+    messages = []
+
+    def handle(ecls, ecode, emsg):
+        messages.append(emsg)
+
+    def log_message(category, message):
+        messages.clear()
+        gdal.Debug(category, message)
+        return messages[0] if messages else None
+
+    log_message.handle = handle
+
+    with gdaltest.error_handler(handle):
+        yield log_message
+
+
+@pytest.mark.parametrize(
+    "booleans",
+    [("YES", "NO"), ("TRUE", "FALSE"), ("ON", "OFF"), ("1", "0")],
+    ids="_".join,
+)
+def test_misc_cpl_debug(debug_output, booleans):
+
+    on, off = booleans
+
+    assert debug_output("GDAL", "msg") is None
+
+    with gdal.config_option("CPL_DEBUG", off):
+        assert debug_output("GDAL", "msg") is None
+
+    with gdal.config_option("CPL_DEBUG", on):
+        assert debug_output("GDAL", "message") == "GDAL: message"
+
+        with gdal.config_option("CPL_TIMESTAMP", off):
+            assert debug_output("GDAL", "message") == "GDAL: message"
+
+        with gdal.config_option("CPL_TIMESTAMP", on):
+            output = debug_output("GDAL", "message")
+            assert str(datetime.datetime.now().year) in output
+            assert output.endswith("GDAL: message")
+
+
+def test_misc_cpl_debug_filtering(debug_output):
+
+    with gdal.config_option("CPL_DEBUG", "GDAL"):
+        assert debug_output("GDAL", "msg") == "GDAL: msg"
+        assert debug_output("GDAL_WARP", "msg") is None
+        assert debug_output("", "msg") == ": msg"
+
+    with gdal.config_option("CPL_DEBUG", "GDAL_WARP_TRANSLATE_ETC"):
+        assert debug_output("GDAL", "msg") == "GDAL: msg"
+        assert debug_output("TRANSLATE", "msg") == "TRANSLATE: msg"
+
+    with gdal.config_option("CPL_DEBUG", ""):
+        assert debug_output("GDAL", "msg") == "GDAL: msg"
+
+
 ###############################################################################
 # Test ConfigureLogging()
 
diff --git a/port/cpl_error.cpp b/port/cpl_error.cpp
index f751837377b0..b25c6511d4aa 100644
--- a/port/cpl_error.cpp
+++ b/port/cpl_error.cpp
@@ -590,11 +590,18 @@ static void CPLvDebug(const char *pszCategory,
     /* -------------------------------------------------------------------- */
     /*      Does this message pass our current criteria?                    */
     /* -------------------------------------------------------------------- */
-    if (pszDebug == nullptr)
+    if (pszDebug == nullptr || EQUAL(pszDebug, "NO") ||
+        EQUAL(pszDebug, "OFF") || EQUAL(pszDebug, "FALSE") ||
+        EQUAL(pszDebug, "0"))
+    {
         return;
+    }
 
-    if (!EQUAL(pszDebug, "ON") && !EQUAL(pszDebug, ""))
+    if (!EQUAL(pszDebug, "ON") && !EQUAL(pszDebug, "YES") &&
+        !EQUAL(pszDebug, "TRUE") && !EQUAL(pszDebug, "1") &&
+        !EQUAL(pszDebug, ""))
     {
+        // check if value of CPL_DEBUG contains the category
         const size_t nLen = strlen(pszCategory);
 
         size_t i = 0;
@@ -623,7 +630,7 @@ static void CPLvDebug(const char *pszCategory,
 
     pszMessage[0] = '\0';
 #ifdef TIMESTAMP_DEBUG
-    if (CPLGetConfigOption("CPL_TIMESTAMP", nullptr) != nullptr)
+    if (CPLTestBool(CPLGetConfigOption("CPL_TIMESTAMP", "NO")))
     {
         static struct CPLTimeVal tvStart;
         static const auto unused = CPLGettimeofday(&tvStart, nullptr);