diff --git a/db/migrate/20260629000001_fix_probe_result_duration_precision.rb b/db/migrate/20260629000001_fix_probe_result_duration_precision.rb
new file mode 100644
index 0000000..c7490a8
--- /dev/null
+++ b/db/migrate/20260629000001_fix_probe_result_duration_precision.rb
@@ -0,0 +1,14 @@
+class FixProbeResultDurationPrecision < ActiveRecord::Migration[8.0]
+  # `t.decimal :duration` with no precision becomes DECIMAL(10,0) on MySQL,
+  # which rounds every duration to a whole second on write. Probe durations
+  # are sub-second floats from a monotonic clock, so they were all stored as
+  # 0. SQLite preserved the fractional value, which is why this only surfaced
+  # after the MySQL migration. Give the column microsecond precision.
+  def up
+    change_column :upright_probe_results, :duration, :decimal, precision: 10, scale: 6
+  end
+
+  def down
+    change_column :upright_probe_results, :duration, :decimal
+  end
+end
diff --git a/test/dummy/db/schema.rb b/test/dummy/db/schema.rb
index c671aa7..6c06c3e 100644
--- a/test/dummy/db/schema.rb
+++ b/test/dummy/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2025_01_14_000001) do
+ActiveRecord::Schema[8.1].define(version: 2026_06_29_000001) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.bigint "blob_id", null: false
     t.datetime "created_at", null: false
@@ -41,7 +41,7 @@
 
   create_table "upright_probe_results", force: :cascade do |t|
     t.datetime "created_at", null: false
-    t.decimal "duration"
+    t.decimal "duration", precision: 10, scale: 6
     t.string "probe_name"
     t.string "probe_service"
     t.string "probe_target"