diff --git a/.changeset/gradient-explicit-optional-args.md b/.changeset/gradient-explicit-optional-args.md
new file mode 100644
index 00000000..a20a3038
--- /dev/null
+++ b/.changeset/gradient-explicit-optional-args.md
@@ -0,0 +1,5 @@
+---
+"@imgproxy/imgproxy-js-core": patch
+---
+
+Fix the `gradient` option dropping optional arguments explicitly set to `0`. `color`, `direction`, `start` and `stop` were checked for truthiness, so `{ gradient: { opacity: 0.5, stop: 0 } }` produced `gr:0.5` and imgproxy fell back to the default `stop` of `1.0` instead of the requested `0`. The same applied to `start: 0` and to a `direction` angle of `0`. These values are now rendered explicitly, and invalid falsy values (such as `null` or an empty `color`) are reported instead of being silently ignored.
diff --git a/src/options/gradient.ts b/src/options/gradient.ts
index 62428728..e0ab4eda 100644
--- a/src/options/gradient.ts
+++ b/src/options/gradient.ts
@@ -30,8 +30,8 @@ const build = (options: GradientOptionsPartial): string => {
     addParam: { min: 0, max: 1 },
   });
 
-  if (color) guardIsNotStr(color, "gradient.color", true);
-  if (direction) {
+  if (color !== undefined) guardIsNotStr(color, "gradient.color", true);
+  if (direction !== undefined) {
     if (typeof direction === "number") {
       guardIsNotNum(direction, "gradient.direction");
     } else {
@@ -39,16 +39,16 @@ const build = (options: GradientOptionsPartial): string => {
       guardIsValidVal(currentDirection, direction, "gradient.direction");
     }
   }
-  if (start)
+  if (start !== undefined)
     guardIsNotNum(start, "gradient.start", { addParam: { min: 0, max: 1 } });
-  if (stop)
+  if (stop !== undefined)
     guardIsNotNum(stop, "gradient.stop", { addParam: { min: 0, max: 1 } });
 
   const op = opacity;
-  const c = color || "";
-  const dir = direction || "";
-  const or = start || "";
-  const end = stop || "";
+  const c = color ?? "";
+  const dir = direction ?? "";
+  const or = start ?? "";
+  const end = stop ?? "";
 
   return `gr:${op}:${c}:${dir}:${or}:${end}`.replace(/:+$/, "");
 };
diff --git a/tests/optionsBasic/gradient.test.ts b/tests/optionsBasic/gradient.test.ts
index ca16257d..a4eb9e6e 100644
--- a/tests/optionsBasic/gradient.test.ts
+++ b/tests/optionsBasic/gradient.test.ts
@@ -190,5 +190,51 @@ describe("gradient", () => {
         })
       ).toEqual("gr:0::::0.85");
     });
+
+    it("should correctly handle 0 stop", () => {
+      expect(
+        build({
+          gradient: {
+            opacity: 0.5,
+            stop: 0,
+          },
+        })
+      ).toEqual("gr:0.5::::0");
+    });
+
+    it("should correctly handle 0 start", () => {
+      expect(
+        build({
+          gradient: {
+            opacity: 0.5,
+            start: 0,
+          },
+        })
+      ).toEqual("gr:0.5:::0");
+    });
+
+    it("should correctly handle 0 direction angle", () => {
+      expect(
+        build({
+          gradient: {
+            opacity: 0.5,
+            direction: 0,
+          },
+        })
+      ).toEqual("gr:0.5::0");
+    });
+
+    it("should throw an error if start is null", () => {
+      expect(() =>
+        // @ts-expect-error: Let's ignore an error (check for users with vanilla js).
+        build({ gradient: { opacity: 0.5, start: null } })
+      ).toThrow("gradient.start is not a number");
+    });
+
+    it("should throw an error if color is an empty string", () => {
+      expect(() => build({ gradient: { opacity: 0.5, color: "" } })).toThrow(
+        "gradient.color must be 3, 6 or 8 characters long (with alpha)"
+      );
+    });
   });
 });