diff --git a/db/migrate/20230731140544_fix_samples_measured_signals.rb b/db/migrate/20230731140544_fix_samples_measured_signals.rb
new file mode 100644
index 000000000..43e41c379
--- /dev/null
+++ b/db/migrate/20230731140544_fix_samples_measured_signals.rb
@@ -0,0 +1,17 @@
+class FixSamplesMeasuredSignals < ActiveRecord::Migration[5.0]
+  def up
+    # make sure measured signals are always a float (the entity framework
+    # deletes the attribute from the core_fields when it's nil):
+    Sample
+      .where("core_fields LIKE '%measured_signal%'")
+      .preload(:sample_identifiers)
+      .find_each do |sample|
+        sample.measured_signal = sample.measured_signal.presence&.to_f
+        sample.save(validate: false)
+      end
+  end
+
+  def down
+    # nothing to do
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index e95e4b4d8..720fc7cea 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20221223203602) do
+ActiveRecord::Schema.define(version: 20230731140544) do
 
   create_table "alert_condition_results", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci" do |t|
     t.string  "result"