diff --git a/.gitignore b/.gitignore
index 53f9e6811..9fe765dfd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -69,3 +69,6 @@ cmake-build*
 # CBMC files
 *.goto
 *.log
+
+# source code for system_info and other test apps
+!bin
diff --git a/bin/system_info/print_system_info.c b/bin/system_info/print_system_info.c
index aac1b570f..5197e5d85 100644
--- a/bin/system_info/print_system_info.c
+++ b/bin/system_info/print_system_info.c
@@ -53,6 +53,12 @@ int main(void) {
     fprintf(stdout, "       'amd_bmi2': %s\n", aws_cpu_has_feature(AWS_CPU_FEATURE_BMI2) ? "true" : "false");
     fprintf(stdout, "   }\n");
 
+#if defined(AWS_USE_CPU_EXTENSIONS)
+    fprintf(stdout, "  'use cpu extensions': true\n");
+#else
+    fprintf(stdout, "  'use cpu extensions': false\n");
+#endif
+
     fprintf(stdout, "}\n");
     aws_system_environment_release(env);
     aws_logger_clean_up(&logger);
diff --git a/bin/system_info/test-print-system-info.py b/bin/system_info/test-print-system-info.py
new file mode 100755
index 000000000..027cf2cf9
--- /dev/null
+++ b/bin/system_info/test-print-system-info.py
@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+import argparse
+import os
+from pathlib import Path
+import platform
+import re
+import subprocess
+from typing import Dict, List, Optional
+
+PARSER = argparse.ArgumentParser(
+    description="Run print-sys-info to detect CPU features. Fail if the results seem wrong.")
+PARSER.add_argument("--print-sys-info-path",
+                    help="Path to print-sys-info app")
+PARSER.add_argument("--build-dir",
+                    help="Search this dir for print-sys-info app")
+
+
+FEATURE_ALIASES = {
+    'avx512': ['avx512f'],
+    'clmul': ['pclmulqdq'],
+    'crc': ['crc32'],
+    'crypto': ['aes'],
+}
+
+
+def main():
+    args = PARSER.parse_args()
+
+    if args.print_sys_info_path:
+        app = Path(args.print_sys_info_path)
+    else:
+        app = find_app(args.build_dir)
+
+    # run print-sys-info. get feature names and whether it thinks they're supported
+    app_features_presence: Dict[str, bool] = detect_features_from_app(app)
+
+    # get feature info from OS (i.e. read /proc/cpuinfo on linux), get back list of supported features
+    os_features_list = detect_features_from_os()
+
+    # For each feature that print-sys-info says was (or wasn't) there,
+    # check the os_features_list and make sure it is (or isn't_ present.
+    for (feature, app_presence) in app_features_presence.items():
+        os_presence = feature in os_features_list
+        if not os_presence:
+            # sometimes a feature has a mildly different name across platforms
+            for alias in FEATURE_ALIASES.get(feature, []):
+                if alias in os_features_list:
+                    os_presence = True
+                    break
+
+        if app_presence != os_presence:
+            exit(f"FAILED: aws-c-common and OS disagree on whether CPU supports feature '{feature}'\n" +
+                 f"\taws-c-common:{app_presence} OS:{os_presence}")
+
+    print("SUCCESS: aws-c-common and OS agree on CPU features")
+
+
+def find_app(build_dir: Optional[str]) -> Path:
+    if build_dir is None:
+        build_dir = find_build_dir()
+    else:
+        build_dir = Path(build_dir).absolute()
+
+    app_name = 'print-sys-info'
+    if os.name == 'nt':
+        app_name = app_name + '.exe'
+
+    for file in build_dir.glob(f"**/{app_name}"):
+        return file
+
+    exit(f"FAILED: Can't find '{app_name}' under: {build_dir}"
+         "\nPass --build-dir to hint location.")
+
+
+def find_build_dir() -> Path:
+    dir = Path(__file__).parent.absolute()
+    while dir is not None:
+        for build_dir in dir.glob('build'):
+            return build_dir
+        dir = dir.parent
+
+    exit("FAILED: Can't find build dir. Pass --build-dir to hint location.")
+
+
+def detect_features_from_app(app_path: Path) -> Dict[str, bool]:
+    result = subprocess.run([str(app_path)],
+                            universal_newlines=True,
+                            stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE)
+    print(f"--- {app_path} ---")
+    print(result.stderr)
+    print(result.stdout)
+    if result.returncode != 0:
+        exit(f"FAILED: {app_path.name} exited with {result.returncode}")
+
+    lines = result.stdout.splitlines()
+
+    machine = platform.machine().lower()
+    if machine in ['x86_64', 'amd64']:
+        machine = 'amd'
+    elif machine.startswith('arm') or machine == 'aarch64':
+        machine = 'arm'
+    else:
+        print(f"SKIP TEST: unknown platform.machine(): {machine}")
+        exit(0)
+
+    # looking for lines like:
+    #        'arm_crypto': true,
+    #        'amd_sse4_1': false
+    features = {}
+    for line in lines:
+        m = re.search(f"'{machine}_(.+)': (false|true)", line)
+        if m:
+            name = m.group(1)
+            is_present = m.group(2) == 'true'
+            features[name] = is_present
+
+    # if aws-c-common compiled with -DUSE_CPU_EXTENSIONS=OFF, skip this this test
+    for line in lines:
+        m = re.search(f"'use cpu extensions': false", line)
+        if m:
+            print("SKIP TEST: aws-c-common compiled with -DUSE_CPU_EXTENSIONS=OFF")
+            exit(0)
+
+    if not features:
+        raise RuntimeError("Cannot find features text in stdout ???")
+
+    return features
+
+
+def detect_features_from_os() -> List[str]:
+    features = []
+
+    cpuinfo_path = '/proc/cpuinfo'
+    try:
+        with open(cpuinfo_path) as f:
+            cpuinfo_text = f.read()
+    except:
+        print(f"SKIP TEST: currently, this test only works on machines with /proc/cpuinfo")
+        exit(0)
+
+    # looking for line like:
+    # flags           : fpu vme de pse ...
+    # OR
+    # features        : fp asimd evtstrm ...
+    print(f"--- {cpuinfo_path} ---")
+    for line in cpuinfo_text.splitlines():
+        line = line.lower()
+        print(line)
+        m = re.match(r"(flags|features)\s+:(.*)", line)
+        if m:
+            features = m.group(2).split()
+            return features
+
+    exit(f"FAILED: Cannot detect CPU features in {cpuinfo_path}")
+
+
+if __name__ == '__main__':
+    main()
diff --git a/builder.json b/builder.json
index cdb127746..e4d50754d 100644
--- a/builder.json
+++ b/builder.json
@@ -19,5 +19,9 @@
                 ["dir", "/s", "/b"]
             ]
         }
-    }
+    },
+    "test_steps": [
+        "test",
+        ["python3", "{source_dir}/bin/system_info/test-print-system-info.py", "--build-dir", "{build_dir}"]
+    ]
 }