diff --git a/src/sentry_os.c b/src/sentry_os.c
index d7cc2d58d6..fefcf01ebb 100644
--- a/src/sentry_os.c
+++ b/src/sentry_os.c
@@ -263,6 +263,30 @@ sentry_set_thread_stack_guarantee(uint32_t stack_guarantee_in_bytes)
     return 1;
 }
 
+// Resolves the handler stack size (in KiB) from the `SENTRY_HANDLER_STACK_SIZE`
+// environment variable, falling back to the compile-time default. This is
+// called from `DllMain` via `sentry__set_default_thread_stack_guarantee`, so
+// it must avoid CRT (`getenv`, `strtod`, ...) and only use kernel32 exports.
+static size_t
+sentry__handler_stack_size_kib(void)
+{
+    char buf[12];
+    DWORD n = GetEnvironmentVariableA(
+        "SENTRY_HANDLER_STACK_SIZE", buf, sizeof(buf));
+    if (n == 0 || n >= sizeof(buf)) {
+        return SENTRY_HANDLER_STACK_SIZE;
+    }
+    size_t val = 0;
+    for (DWORD i = 0; i < n; i++) {
+        if (buf[i] < '0' || buf[i] > '9') {
+            return SENTRY_HANDLER_STACK_SIZE;
+        }
+        val = val * 10 + (size_t)(buf[i] - '0');
+    }
+    return (val > 0 && val <= 0xFFFFFFFFu / 1024) ? val
+                                                  : SENTRY_HANDLER_STACK_SIZE;
+}
+
 void
 sentry__set_default_thread_stack_guarantee(void)
 {
@@ -270,8 +294,9 @@ sentry__set_default_thread_stack_guarantee(void)
         return;
     }
 
+    const size_t stack_size_kib = sentry__handler_stack_size_kib();
     const unsigned long expected_stack_guarantee
-        = SENTRY_HANDLER_STACK_SIZE * 1024;
+        = (unsigned long)stack_size_kib * 1024;
     DWORD thread_id = GetThreadId(GetCurrentThread());
     ULONG_PTR high = 0;
     ULONG_PTR low = 0;
@@ -284,8 +309,7 @@ sentry__set_default_thread_stack_guarantee(void)
         SENTRY_WARNF(
             "Cannot set handler stack guarantee of %zuKiB for thread %lu "
             "(stack reserve: %zuKiB, expected factor: %zux, actual: %.2fx)",
-            (size_t)SENTRY_HANDLER_STACK_SIZE, thread_id,
-            thread_stack_reserve / 1024,
+            stack_size_kib, thread_id, thread_stack_reserve / 1024,
             (size_t)SENTRY_THREAD_STACK_GUARANTEE_FACTOR,
             expected_stack_reserve / (double)expected_stack_guarantee);
         return;
diff --git a/tests/test_integration_crashpad.py b/tests/test_integration_crashpad.py
index a2dca88174..adaf3ccff7 100644
--- a/tests/test_integration_crashpad.py
+++ b/tests/test_integration_crashpad.py
@@ -440,18 +440,18 @@ def test_crashpad_dumping_crash(cmake, httpserver, run_args, build_args):
 
 
 @pytest.mark.parametrize(
-    "build_args",
+    "stack_size",
     [
-        ({}),  # uses default of 64KiB
+        None,  # uses default of 64KiB
         pytest.param(
-            {"SENTRY_HANDLER_STACK_SIZE": "16"},
+            "16",
             marks=pytest.mark.skipif(
                 sys.platform != "win32",
                 reason="handler stack size parameterization tests stack guarantee on windows only",
             ),
         ),
         pytest.param(
-            {"SENTRY_HANDLER_STACK_SIZE": "32"},
+            "32",
             marks=pytest.mark.skipif(
                 sys.platform != "win32",
                 reason="handler stack size parameterization tests stack guarantee on windows only",
@@ -459,11 +459,12 @@ def test_crashpad_dumping_crash(cmake, httpserver, run_args, build_args):
         ),
     ],
 )
-def test_crashpad_dumping_stack_overflow(cmake, httpserver, build_args):
-    build_args.update({"SENTRY_BACKEND": "crashpad"})
-    tmp_path = cmake(["sentry_example"], build_args)
+def test_crashpad_dumping_stack_overflow(cmake, httpserver, stack_size):
+    tmp_path = cmake(["sentry_example"], {"SENTRY_BACKEND": "crashpad"})
 
     env = dict(os.environ, SENTRY_DSN=make_dsn(httpserver))
+    if stack_size:
+        env["SENTRY_HANDLER_STACK_SIZE"] = stack_size
     httpserver.expect_oneshot_request("/api/123456/minidump/").respond_with_data("OK")
     httpserver.expect_request("/api/123456/envelope/").respond_with_data("OK")
 
diff --git a/tests/test_integration_stdout.py b/tests/test_integration_stdout.py
index ecbdac1a5c..83ff40656a 100644
--- a/tests/test_integration_stdout.py
+++ b/tests/test_integration_stdout.py
@@ -158,13 +158,13 @@ def test_multi_process(cmake):
     assert len(runs) == 0
 
 
-def run_stdout_for(backend, cmake, example_args, build_args=None):
+def run_stdout_for(backend, cmake, example_args, build_args=None, env=None):
     build_args = dict(build_args or {})
     build_args.update({"SENTRY_BACKEND": backend, "SENTRY_TRANSPORT": "none"})
 
     tmp_path = cmake(["sentry_example"], build_args)
 
-    run(tmp_path, "sentry_example", example_args, expect_failure=True)
+    run(tmp_path, "sentry_example", example_args, expect_failure=True, env=env)
 
     return tmp_path, check_output(tmp_path, "sentry_example", ["stdout", "no-setup"])
 
@@ -243,12 +243,12 @@ def test_inproc_crash_stdout_before_send_and_on_crash(cmake):
 
 
 @pytest.mark.parametrize(
-    "build_args",
+    "stack_size",
     [
-        ({}),  # uses default of 64KiB
+        None,  # uses default of 64KiB
         # no test with 16KiB since `inproc` fails with that handler stack size
         pytest.param(
-            {"SENTRY_HANDLER_STACK_SIZE": "32"},
+            "32",
             marks=pytest.mark.skipif(
                 sys.platform != "win32",
                 reason="handler stack size parameterization tests stack guarantee on windows only",
@@ -256,9 +256,12 @@ def test_inproc_crash_stdout_before_send_and_on_crash(cmake):
         ),
     ],
 )
-def test_inproc_stack_overflow_stdout(cmake, build_args):
+def test_inproc_stack_overflow_stdout(cmake, stack_size):
+    env = dict(os.environ)
+    if stack_size:
+        env["SENTRY_HANDLER_STACK_SIZE"] = stack_size
     tmp_path, output = run_stdout_for(
-        "inproc", cmake, ["log", "attachment", "stack-overflow"], build_args
+        "inproc", cmake, ["log", "attachment", "stack-overflow"], env=env
     )
 
     envelope = Envelope.deserialize(output)
@@ -328,18 +331,18 @@ def test_breakpad_crash_stdout_before_send_and_on_crash(cmake):
 
 
 @pytest.mark.parametrize(
-    "build_args",
+    "stack_size",
     [
-        ({}),  # uses default of 64KiB
+        None,  # uses default of 64KiB
         pytest.param(
-            {"SENTRY_HANDLER_STACK_SIZE": "16"},
+            "16",
             marks=pytest.mark.skipif(
                 sys.platform != "win32",
                 reason="handler stack size parameterization tests stack guarantee on windows only",
             ),
         ),
         pytest.param(
-            {"SENTRY_HANDLER_STACK_SIZE": "32"},
+            "32",
             marks=pytest.mark.skipif(
                 sys.platform != "win32",
                 reason="handler stack size parameterization tests stack guarantee on windows only",
@@ -348,9 +351,12 @@ def test_breakpad_crash_stdout_before_send_and_on_crash(cmake):
     ],
 )
 @pytest.mark.skipif(not has_breakpad, reason="test needs breakpad backend")
-def test_breakpad_stack_overflow_stdout(cmake, build_args):
+def test_breakpad_stack_overflow_stdout(cmake, stack_size):
+    env = dict(os.environ)
+    if stack_size:
+        env["SENTRY_HANDLER_STACK_SIZE"] = stack_size
     tmp_path, output = run_stdout_for(
-        "breakpad", cmake, ["attachment", "stack-overflow"], build_args
+        "breakpad", cmake, ["attachment", "stack-overflow"], env=env
     )
 
     envelope = Envelope.deserialize(output)