diff --git a/SConstruct b/SConstruct
index 6e56617..cb747f4 100644
--- a/SConstruct
+++ b/SConstruct
@@ -133,6 +133,14 @@ vars.Add(BoolVariable(
 vars.Add(BoolVariable(
     'with_shared_cctbx',
     'compile and link with the shared cctbx library', False))
+vars.Add(
+    'arch',
+    'target CPU passed to -march in the \'fast\' build. Empty (the default) means '
+    'no -march => maximum portability. Set \'x86-64-v3\' for a portable AVX2/FMA '
+    'build (Intel Haswell 2013+, AMD Zen 2017+), \'native\' for a machine-specific '
+    'build, or \'x86-64-v4\' for AVX-512. Also settable via the OBJCRYST_ARCH '
+    'environment variable.',
+    os.environ.get('OBJCRYST_ARCH', ''))
 
 vars.Update(env)
 env.Help(MY_SCONS_HELP % vars.GenerateHelpText(env))
diff --git a/src/SConscript b/src/SConscript
index 53d5887..98fdde7 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -44,6 +44,8 @@ else:
         # g++ options
         env.PrependUnique(CCFLAGS=['-Wall'])
         fast_optimflags = ['-ffast-math']
+        if env.get('arch'):
+            fast_optimflags.append('-march=' + env['arch'])
 
     # Configure build variants
     if env['build'] == 'debug':