diff --git a/lib/spack/llnl/util/cpu/microarchitectures.json b/lib/spack/llnl/util/cpu/microarchitectures.json
index 2e20cc98f8..ad985ba994 100644
--- a/lib/spack/llnl/util/cpu/microarchitectures.json
+++ b/lib/spack/llnl/util/cpu/microarchitectures.json
@@ -49,11 +49,18 @@
       "vendor": "generic",
       "features": [],
       "compilers": {
-        "gcc": {
-          "versions": "4:",
-          "name": "x86-64",
-          "flags": "-march={name} -mtune={name}"
-        }
+        "gcc": [
+          {
+            "versions": "4.2.0:",
+            "name": "x86-64",
+            "flags": "-march={name} -mtune=generic"
+          },
+          {
+            "versions": "4.0:4.1.2",
+            "name": "x86-64",
+            "flags": "-march={name} -mtune={name}"
+          }
+        ]
       }
     },
     "nocona": {
diff --git a/lib/spack/spack/test/llnl/util/cpu.py b/lib/spack/spack/test/llnl/util/cpu.py
index 836514cc3c..9af784d103 100644
--- a/lib/spack/spack/test/llnl/util/cpu.py
+++ b/lib/spack/spack/test/llnl/util/cpu.py
@@ -190,7 +190,9 @@ def test_target_json_schema():
 
 
 @pytest.mark.parametrize('target_name,compiler,version,expected_flags', [
-    ('x86_64', 'gcc', '4.9.3', '-march=x86-64 -mtune=x86-64'),
+    ('x86_64', 'gcc', '4.9.3', '-march=x86-64 -mtune=generic'),
+    ('x86_64', 'gcc', '4.2.0', '-march=x86-64 -mtune=generic'),
+    ('x86_64', 'gcc', '4.1.1', '-march=x86-64 -mtune=x86-64'),
     ('nocona', 'gcc', '4.9.3', '-march=nocona -mtune=nocona'),
     ('nehalem', 'gcc', '4.9.3', '-march=nehalem -mtune=nehalem'),
     ('nehalem', 'gcc', '4.8.5', '-march=corei7 -mtune=corei7'),