diff --git a/src/include/patomic/internal/align.h b/src/include/patomic/internal/align.h
index d0a2675a0..3c142066f 100644
--- a/src/include/patomic/internal/align.h
+++ b/src/include/patomic/internal/align.h
@@ -12,6 +12,10 @@
  *
  * @details
  *   Priority is given to "recommended", then "minimum", then "size_within".
+ *
+ * @return
+ *   Returns -1 if lhs is a looser requirement than rhs, 1 if lhs is a stricter
+ *   requirement than rhs, otherwise 0.
  */
 int
 patomic_internal_compare_align(
diff --git a/test/kind/ut/CMakeLists.txt b/test/kind/ut/CMakeLists.txt
index fe6d8adb6..4194fd724 100644
--- a/test/kind/ut/CMakeLists.txt
+++ b/test/kind/ut/CMakeLists.txt
@@ -2,3 +2,6 @@
 
 add_custom_target(${test_target_name}-ut)
 add_dependencies(${test_target_name} ${test_target_name}-ut)
+
+# add all subdirectories
+add_subdirectory(api)
diff --git a/test/kind/ut/api/CMakeLists.txt b/test/kind/ut/api/CMakeLists.txt
new file mode 100644
index 000000000..2f715fdaa
--- /dev/null
+++ b/test/kind/ut/api/CMakeLists.txt
@@ -0,0 +1,8 @@
+# ---- Create Tests ----
+
+create_ut(
+    NAME UtApiAlign
+    SOURCE
+        align.cpp
+        "${PATOMIC_SOURCE_DIR}/src/api/align.c"
+)
diff --git a/test/kind/ut/api/align.cpp b/test/kind/ut/api/align.cpp
new file mode 100644
index 000000000..6734d4923
--- /dev/null
+++ b/test/kind/ut/api/align.cpp
@@ -0,0 +1,75 @@
+extern "C" {
+#include <patomic/internal/align.h>
+};
+
+#include <gtest/gtest.h>
+
+
+/// @brief Test fixture.
+class UtApiAlign : public testing::Test
+{};
+
+
+/// @brief Comparing patomic_align_t prioritizes recommend over all other
+///        members.
+TEST_F(UtApiAlign, compare_align_recommended_ne)
+{
+    // setup
+    // larger recommended is stricter
+    patomic_align_t lt { 1, 16, 16 };
+    patomic_align_t gt { 2, 8, 8 };
+
+    // test
+    // check values
+    EXPECT_LT(lt.recommended, gt.recommended);
+    EXPECT_GT(lt.minimum, gt.minimum);
+    EXPECT_GT(lt.size_within, gt.size_within);
+    // do comparison
+    EXPECT_LT(patomic_internal_compare_align(lt, gt), 0);
+    EXPECT_GT(patomic_internal_compare_align(gt, lt), 0);
+}
+
+/// @brief Comparing patomic_align_t prioritizes minimum over all other members
+///        if recommend compares equal.
+TEST_F(UtApiAlign, compare_align_minimum_ne_recommended_eq)
+{
+    // setup
+    // larger recommended is stricter
+    patomic_align_t lt { 64, 1, 16 };
+    patomic_align_t gt { 64, 2, 8 };
+
+    // test
+    // check values
+    EXPECT_EQ(lt.recommended, gt.recommended);
+    EXPECT_LT(lt.minimum, gt.minimum);
+    EXPECT_GT(lt.size_within, gt.size_within);
+    // do comparison
+    EXPECT_LT(patomic_internal_compare_align(lt, gt), 0);
+    EXPECT_GT(patomic_internal_compare_align(gt, lt), 0);
+}
+
+/// @brief Comparing patomic_align_t prioritizes size_within after all other
+///        members.
+TEST_F(UtApiAlign, compare_align_size_within_any_minimum_eq_recommended_eq)
+{
+    // setup
+    // smaller size_within is stricter (except zero which is least strict)
+    patomic_align_t zero { 64, 32, 0 };
+    patomic_align_t lt { 64, 32, 2 };
+    patomic_align_t gt { 64, 32, 1 };
+
+    // test
+    // check values
+    EXPECT_EQ(0, zero.size_within);
+    EXPECT_EQ(lt.recommended, gt.recommended);
+    EXPECT_EQ(lt.minimum, gt.minimum);
+    EXPECT_GT(lt.size_within, gt.size_within);
+    // do comparison
+    EXPECT_EQ(patomic_internal_compare_align(zero, zero), 0);
+    EXPECT_EQ(patomic_internal_compare_align(lt, lt), 0);
+    EXPECT_EQ(patomic_internal_compare_align(gt, gt), 0);
+    EXPECT_LT(patomic_internal_compare_align(zero, lt), 0);
+    EXPECT_LT(patomic_internal_compare_align(lt, gt), 0);
+    EXPECT_GT(patomic_internal_compare_align(gt, lt), 0);
+    EXPECT_GT(patomic_internal_compare_align(lt, zero), 0);
+}