diff --git a/pyproject.toml b/pyproject.toml
index 852a2b7..eb46ac3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,9 +10,12 @@ license-files = ["LICENSE"]
 requires-python = ">=3.13"
 dependencies = [
     "dropbox>=12.0.2",
-    "flet>=0.85.3",
-    "flet-permission-handler>=0.85.3",
-    "flet-secure-storage>=0.85.3",
+    # Pin exact: `flet build` resolves deps from pyproject (not uv.lock). A
+    # newer Python `flet` with an older Flutter client (or vice versa) breaks
+    # the wire protocol and the packaged app stays on a black screen.
+    "flet==0.85.3",
+    "flet-permission-handler==0.85.3",
+    "flet-secure-storage==0.85.3",
     "garmin-fit-sdk>=21.208.0",
     "packaging>=26.2",
     "platformdirs>=4.0",
diff --git a/uv.lock b/uv.lock
index 539142d..3d87ca9 100644
--- a/uv.lock
+++ b/uv.lock
@@ -230,9 +230,9 @@ dev = [
 [package.metadata]
 requires-dist = [
     { name = "dropbox", specifier = ">=12.0.2" },
-    { name = "flet", specifier = ">=0.85.3" },
-    { name = "flet-permission-handler", specifier = ">=0.85.3" },
-    { name = "flet-secure-storage", specifier = ">=0.85.3" },
+    { name = "flet", specifier = "==0.85.3" },
+    { name = "flet-permission-handler", specifier = "==0.85.3" },
+    { name = "flet-secure-storage", specifier = "==0.85.3" },
     { name = "garmin-fit-sdk", specifier = ">=21.208.0" },
     { name = "packaging", specifier = ">=26.2" },
     { name = "platformdirs", specifier = ">=4.0" },