diff --git a/brewman/alembic/versions/6fb6c96fd408_prevent_duplicate_attendance.py b/brewman/alembic/versions/6fb6c96fd408_prevent_duplicate_attendance.py
new file mode 100644
index 00000000..9250acf6
--- /dev/null
+++ b/brewman/alembic/versions/6fb6c96fd408_prevent_duplicate_attendance.py
@@ -0,0 +1,35 @@
+"""att
+
+Revision ID: 6fb6c96fd408
+Revises: 071e8f29d257
+Create Date: 2021-09-11 17:03:39.649878
+
+"""
+import sqlalchemy as sa
+
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision = "6fb6c96fd408"
+down_revision = "071e8f29d257"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_index(
+        "only_one_valid_attendance",
+        "attendances",
+        ["employee_id", "date"],
+        unique=True,
+        postgresql_where=sa.text("is_valid = true"),
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index("only_one_valid_attendance", table_name="attendances", postgresql_where=sa.text("is_valid = true"))
+    # ### end Alembic commands ###
diff --git a/brewman/brewman/models/attendance.py b/brewman/brewman/models/attendance.py
index 8b93c739..d3499e02 100644
--- a/brewman/brewman/models/attendance.py
+++ b/brewman/brewman/models/attendance.py
@@ -8,6 +8,7 @@ from sqlalchemy import (
     Date,
     DateTime,
     ForeignKey,
+    Index,
     Integer,
     Numeric,
     select,
@@ -20,7 +21,6 @@ from .meta import Base
 
 class Attendance(Base):
     __tablename__ = "attendances"
-
     id = Column("id", UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
     employee_id = Column("employee_id", UUID(as_uuid=True), ForeignKey("employees.id"))
     date = Column("date", Date, nullable=False)
@@ -30,6 +30,15 @@ class Attendance(Base):
     user_id = Column("user_id", UUID(as_uuid=True), ForeignKey("users.id"))
     is_valid = Column("is_valid", Boolean)
 
+    __table_args__ = (
+        Index(
+            "only_one_valid_attendance",
+            employee_id,
+            date,
+            unique=True,
+            postgresql_where=(is_valid == True),  # noqa: E712
+        ),
+    )
     user = relationship("User", primaryjoin="User.id==Attendance.user_id")
 
     def __init__(
diff --git a/overlord/package.json b/overlord/package.json
index e6feed4b..310ca554 100644
--- a/overlord/package.json
+++ b/overlord/package.json
@@ -48,7 +48,6 @@
     "@angular/compiler-cli": "^12.2.4",
     "@angular/language-service": "^12.2.4",
     "@types/jasmine": "~3.7.4",
-    "@types/mathjs": "^9.4.2",
     "@types/node": "^16.7.10",
     "@typescript-eslint/eslint-plugin": "4.30.0",
     "@typescript-eslint/parser": "4.30.0",