diff --git a/rtree-capi/src/rtree.rs b/rtree-capi/src/rtree.rs
index 17d8651..4587154 100644
--- a/rtree-capi/src/rtree.rs
+++ b/rtree-capi/src/rtree.rs
@@ -223,7 +223,7 @@ pub extern "C" fn rtree_depth(tree: *const RTreeH, depth_out: *mut usize) -> RTr
         return RTreeError::Success;
     }
     let depth = match rtree {
-        RTreeDim::D1(tree) => _interval_tree_depth(tree.root().unwrap()),
+        RTreeDim::D1(tree) => _interval_tree_depth(tree.root().unwrap()) + 1,
         RTreeDim::D2(tree) => _rtree_depth(tree.root()),
         RTreeDim::D3(tree) => _rtree_depth(tree.root()),
     };
diff --git a/rtree-capi/tests/test.c b/rtree-capi/tests/test.c
index 798d54a..175009c 100644
--- a/rtree-capi/tests/test.c
+++ b/rtree-capi/tests/test.c
@@ -264,8 +264,8 @@ bool test_rtree_1d(void) {
     // test rtree_depth
     size_t depth = 0;
     rtree_depth(tree, &depth);
-    if (depth != 1) {
-        fprintf(stderr, "Expected tree depth 1, got %zu\n", depth);
+    if (depth != 2) {
+        fprintf(stderr, "Expected tree depth 2, got %zu\n", depth);
         rtree_free(tree);
         return false;
     }
@@ -595,6 +595,110 @@ bool test_rtree_empty_1d(void) {
     return true;
 }
 
+bool test_rtree_singleton_depth(void) {
+    const size_t N = 1;
+    const uint32_t dim = 2;
+    double mins[2] = {0.0, 0.0};
+    double maxs[2] = {1.0, 1.0};
+    size_t ids[1] = {1};
+    RTreeH *tree = NULL;
+    rtree_bulk_load(&tree, mins, maxs, ids, N, dim);
+    if (tree == NULL) {
+        fprintf(stderr, "Expected to create tree, got null pointer\n");
+        return false;
+    }
+
+    // test rtree_depth
+    size_t depth = 0;
+    rtree_depth(tree, &depth);
+    if (depth != 1) {
+        fprintf(stderr, "Expected tree depth 1 for singleton tree, got %zu\n", depth);
+        rtree_free(tree);
+        return false;
+    }
+    rtree_free(tree);
+
+    const uint32_t dim1d = 1;
+    double mins1d[1] = {0.0};
+    double maxs1d[1] = {1.0};
+    RTreeH *tree1d = NULL;
+    rtree_bulk_load(&tree1d, mins1d, maxs1d, ids, N, dim1d);
+    if (tree1d == NULL) {
+        fprintf(stderr, "Expected to create 1d tree, got null pointer\n");
+        return false;
+    }
+
+    size_t depth1d = 0;
+    rtree_depth(tree1d, &depth1d);
+    if (depth1d != 1) {
+        fprintf(stderr, "Expected tree depth 1 for singleton 1d tree, got %zu\n", depth1d);
+        rtree_free(tree1d);
+        return false;
+    }
+    rtree_free(tree1d);
+
+    return true;
+}
+
+bool test_rtree_depth(void) {
+    // Default MAX_SIZE is 6, so bulk loading 6 should create a tree of depth 1,
+    // while bulk loading 7 should create a tree of depth 2.
+    const size_t N = 6;
+    const uint32_t dim = 2;
+    double mins[12];
+    double maxs[12];
+    size_t ids[6];
+    for (size_t i = 0; i < N; i++) {
+        mins[2*i] = (double)i;
+        mins[2*i + 1] = (double)i;
+        maxs[2*i] = (double)i + 0.5;
+        maxs[2*i + 1] = (double)i + 0.5;
+        ids[i] = i + 1;
+    }
+    RTreeH *tree = NULL;
+    rtree_bulk_load(&tree, mins, maxs, ids, N, dim);
+    if (tree == NULL) {
+        fprintf(stderr, "Expected to create tree, got null pointer\n");
+        return false;
+    }
+    size_t depth = 0;
+    rtree_depth(tree, &depth);
+    if (depth != 1) {
+        fprintf(stderr, "Expected tree depth 1 for 6 items, got %zu\n", depth);
+        rtree_free(tree);
+        return false;
+    }
+    rtree_free(tree);
+
+    const size_t N1 = 7;
+    double mins1[14];
+    double maxs1[14];
+    size_t ids1[7];
+    for (size_t i = 0; i < N1; i++) {
+        mins1[2*i] = (double)i;
+        mins1[2*i + 1] = (double)i;
+        maxs1[2*i] = (double)i + 0.5;
+        maxs1[2*i + 1] = (double)i + 0.5;
+        ids1[i] = i + 1;
+    }
+    RTreeH *tree1 = NULL;
+    rtree_bulk_load(&tree1, mins1, maxs1, ids1, N1, dim);
+    if (tree1 == NULL) {
+        fprintf(stderr, "Expected to create tree, got null pointer\n");
+        return false;
+    }
+    size_t depth1 = 0;
+    rtree_depth(tree1, &depth1);
+    if (depth1 != 2) {
+        fprintf(stderr, "Expected tree depth 2 for 7 items, got %zu\n", depth1);
+        rtree_free(tree1);
+        return false;
+    }
+
+    rtree_free(tree1);
+    return true;
+}
+
 void run_test(
     bool (test)(void),
     const char *test_name,
@@ -621,6 +725,8 @@ int main(void) {
     run_test(test_rtree_empty, "test_rtree_empty", &passed);
     run_test(test_rtree_empty_1d, "test_rtree_empty_1d", &passed);
     run_test(test_invalid_dimension, "test_invalid_dimension", &passed);
+    run_test(test_rtree_singleton_depth, "test_rtree_singleton_depth", &passed);
+    run_test(test_rtree_depth, "test_rtree_depth", &passed);
 
     if (passed) {
         fprintf(stdout, "All tests passed\n");