diff --git a/releasenotes/notes/add-metadata-unique-constraints-dbee79c2ffedc365.yaml b/releasenotes/notes/add-metadata-unique-constraints-dbee79c2ffedc365.yaml
new file mode 100644
index 0000000..ab60441
--- /dev/null
+++ b/releasenotes/notes/add-metadata-unique-constraints-dbee79c2ffedc365.yaml
@@ -0,0 +1,3 @@
+---
+upgrade:
+  - A new migration is added to add unique constraints on the metadata tables.
diff --git a/subunit2sql/db/models.py b/subunit2sql/db/models.py
index 476e4e5..1de38af 100644
--- a/subunit2sql/db/models.py
+++ b/subunit2sql/db/models.py
@@ -110,7 +110,9 @@ class TestRun(BASE, SubunitBase):
 class RunMetadata(BASE, SubunitBase):
     __tablename__ = 'run_metadata'
     __table_args__ = (sa.Index('ix_run_key_value', 'key', 'value'),
-                      sa.Index('ix_run_id', 'run_id'))
+                      sa.Index('ix_run_id', 'run_id'),
+                      sa.UniqueConstraint('run_id', 'key', 'value',
+                                          name='uq_run_metadata'))
 
     id = sa.Column(sa.BigInteger, primary_key=True)
     key = sa.Column(sa.String(255))
@@ -123,7 +125,9 @@ class RunMetadata(BASE, SubunitBase):
 class TestRunMetadata(BASE, SubunitBase):
     __tablename__ = 'test_run_metadata'
     __table_args__ = (sa.Index('ix_test_run_key_value', 'key', 'value'),
-                      sa.Index('ix_test_run_id', 'test_run_id'))
+                      sa.Index('ix_test_run_id', 'test_run_id'),
+                      sa.UniqueConstraint('test_run_id', 'key', 'value',
+                                          name='uq_test_run_metadata'))
 
     id = sa.Column(sa.BigInteger, primary_key=True)
     key = sa.Column(sa.String(255))
@@ -138,7 +142,9 @@ class TestRunMetadata(BASE, SubunitBase):
 class TestMetadata(BASE, SubunitBase):
     __tablename__ = 'test_metadata'
     __table_args__ = (sa.Index('ix_test_key_value', 'key', 'value'),
-                      sa.Index('ix_test_id', 'test_id'))
+                      sa.Index('ix_test_id', 'test_id'),
+                      sa.UniqueConstraint('test_id', 'key', 'value',
+                                          name='uq_test_metadata'))
 
     id = sa.Column(sa.BigInteger, primary_key=True)
     key = sa.Column(sa.String(255))
diff --git a/subunit2sql/migrations/versions/10a2b6d4b06e_add_even_more_indexes.py b/subunit2sql/migrations/versions/10a2b6d4b06e_add_even_more_indexes.py
new file mode 100644
index 0000000..76c52ef
--- /dev/null
+++ b/subunit2sql/migrations/versions/10a2b6d4b06e_add_even_more_indexes.py
@@ -0,0 +1,44 @@
+# Copyright (c) 2015 Hewlett-Packard Development Company, L.P.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Add even more indexes
+
+Revision ID: 10a2b6d4b06e
+Revises: 35cd45895e56
+Create Date: 2015-12-01 18:19:11.328298
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '10a2b6d4b06e'
+down_revision = '35cd45895e56'
+
+from alembic import op
+
+
+def upgrade():
+    with op.batch_alter_table('run_metadata') as batch_op:
+        batch_op.create_unique_constraint('uq_run_metadata',
+                                          ['run_id', 'key', 'value'])
+    with op.batch_alter_table('test_metadata') as batch_op:
+        batch_op.create_unique_constraint('uq_test_metadata',
+                                          ['test_id', 'key', 'value'])
+    with op.batch_alter_table('test_run_metadata') as batch_op:
+        batch_op.create_unique_constraint('uq_test_run_metadata',
+                                          ['test_run_id', 'key', 'value'])
+
+
+def downgrade():
+    NotImplementedError()