diff --git a/_pytest/config.py b/_pytest/config.py
index 22bf6c60c..544c260ee 100644
--- a/_pytest/config.py
+++ b/_pytest/config.py
@@ -1192,12 +1192,15 @@ class Config(object):
         # and -o foo1=bar1 -o foo2=bar2 options
         # always use the last item if multiple value set for same ini-name,
         # e.g. -o foo=bar1 -o foo=bar2 will set foo to bar2
+        first_override_set = False
         for ini_config_list in self._override_ini:
             for ini_config in ini_config_list:
                 try:
                     (key, user_ini_value) = ini_config.split("=", 1)
+                    first_override_set = True
                 except ValueError:
-                    raise UsageError("-o/--override-ini expects option=value style.")
+                    if not first_override_set:
+                        raise UsageError("-o/--override-ini expects option=value style.")
                 if key == name:
                     value = user_ini_value
         return value
diff --git a/testing/test_config.py b/testing/test_config.py
index 44b8c317a..f958b5890 100644
--- a/testing/test_config.py
+++ b/testing/test_config.py
@@ -860,3 +860,40 @@ class TestOverrideIniArgs(object):
         config = get_config()
         config._preparse([], addopts=True)
         assert config._override_ini == [['cache_dir=%s' % cache_dir]]
+
+    def test_all_the_things(self, testdir):
+        testdir.makeconftest("""
+        def pytest_addoption(parser):
+            addini = parser.addini
+            addini("custom_option_1", "", default="o1")
+            addini("custom_option_2", "", default="o2")""")
+        testdir.makepyfile("""
+            def test_multiple_options(pytestconfig):
+                prefix = "custom_option"
+                for x in range(1, 3):
+                    ini_value=pytestconfig.getini("%s_%d" % (prefix, x))
+                    print('\\nini%d:%s' % (x, ini_value))""")
+
+        result = testdir.runpytest(
+            "--override-ini", 'custom_option_1=fulldir=/tmp/user1',
+            'custom_option_2=url=/tmp/user2?a=b&d=e',
+            "test_all_the_things.py")
+        assert "ERROR: -o/--override-ini expects option=value style." not in result.stderr.str()
+
+    def test_throw_exception_if_not_value_pair(self, testdir):
+        testdir.makeconftest("""
+        def pytest_addoption(parser):
+            addini = parser.addini
+            addini("custom_option_1", "", default="o1")
+            addini("custom_option_2", "", default="o2")""")
+        testdir.makepyfile("""
+            def test_multiple_options(pytestconfig):
+                prefix = "custom_option"
+                for x in range(1, 3):
+                    ini_value=pytestconfig.getini("%s_%d" % (prefix, x))
+                    print('\\nini%d:%s' % (x, ini_value))""")
+
+        result = testdir.runpytest(
+            "--override-ini", 'custom_option_1',
+            "test_all_the_things.py")
+        assert "ERROR: -o/--override-ini expects option=value style." in result.stderr.str()