diff --git a/.github/workflows/test-macos.yml b/.github/workflows/test-macos.yml
index b46d154c0..2f6124854 100644
--- a/.github/workflows/test-macos.yml
+++ b/.github/workflows/test-macos.yml
@@ -8,11 +8,12 @@ on:
 
 jobs:
   tests:
-    name: Test Compile ${{ matrix.build_type }}
-    runs-on: macos-latest
+    name: ${{ matrix.build_type }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
 
     strategy:
       matrix:
+        os: [macos-12, macos-13, macos-latest]
         build_type: ["Debug", "Release"]
 
     steps:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d29dd51d9..1a2927753 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,10 +6,13 @@ The public API of this library consists of the functions declared in file
 [h3api.h.in](./src/h3lib/include/h3api.h.in).
 
 ## [Unreleased]
+### Fixed
+- Fixed compacting all or many resolution 1 cells (#919)
+
 ### Changed
 - Replace internal algorithm for `polygonToCells` with a new version that is more memory-efficient (#785)
 - Reorganize tests into public / internal. (#762)
-- Performance enhancement for aarch64, may improve other platforms (#790, #792, #852, #905)
+- Performance enhancement for aarch64, may improve other platforms (#790, #792, #852, #905, #913)
 - `clang-format` upgraded to version 14. (#834)
 - Fixed tests that incorrectly did not test resolution 15. (#820)
 - Use `CMAKE_INSTALL_LIBDIR` when choosing where to install library files. (#819)
diff --git a/src/apps/testapps/testCompactCells.c b/src/apps/testapps/testCompactCells.c
index 56ae5baee..bab73abc2 100644
--- a/src/apps/testapps/testCompactCells.c
+++ b/src/apps/testapps/testCompactCells.c
@@ -106,17 +106,58 @@ SUITE(compactCells) {
         t_assertSuccess(
             H3_EXPORT(uncompactCells)(cells0, numRes0, cells1, numRes1, 1));
 
-        // Fails at compactCells.
-        // However:
-        //   Passes if numUncompacted <= 40
-        //   Fails  if numUncompacted >= 41.
         int64_t numUncompacted = numRes1;
         t_assertSuccess(H3_EXPORT(compactCells)(cells1, out, numUncompacted));
 
-        // TODO: check that output matches cells0
+        // Assert that the output of this function matches exactly the set of
+        // res 0 cells
+        size_t foundCount = 0;
+        for (size_t res1Idx = 0; res1Idx < numRes1; res1Idx++) {
+            H3Index compactedCell = out[res1Idx];
+
+            if (compactedCell) {
+                for (size_t res1DupIdx = 0; res1DupIdx < res1Idx;
+                     res1DupIdx++) {
+                    t_assert(out[res1DupIdx] != compactedCell,
+                             "Duplicated output found");
+                }
+
+                bool found = false;
+                for (size_t res0Idx = 0; res0Idx < numRes0; res0Idx++) {
+                    if (cells0[res0Idx] == compactedCell) {
+                        found = true;
+                        break;
+                    }
+                }
+                t_assert(found, "Res 0 cell is found");
+                foundCount++;
+            }
+        }
+        t_assert(foundCount == numRes0, "all res 0 cells found");
+
+        free(cells0);
+        free(cells1);
+        free(out);
+    }
+
+    TEST(allRes1_variousRanges) {
+        const int64_t numRes0 = 122;
+        const int64_t numRes1 = 842;
+        H3Index *cells0 = calloc(numRes0, sizeof(H3Index));
+        H3Index *cells1 = calloc(numRes1, sizeof(H3Index));
+        H3Index *out = calloc(numRes1, sizeof(H3Index));
+
+        H3_EXPORT(getRes0Cells)(cells0);
+        t_assert(cells0[0] == 0x8001fffffffffff,
+                 "got expected first res0 cell");
+
+        t_assertSuccess(
+            H3_EXPORT(uncompactCells)(cells0, numRes0, cells1, numRes1, 1));
 
+        // Test various (but not all possible combinations) ranges of res 1
+        // cells
         for (int64_t offset = 0; offset < numRes1; offset++) {
-            for (numUncompacted = numRes1 - offset; numUncompacted >= 0;
+            for (int64_t numUncompacted = numRes1 - offset; numUncompacted >= 0;
                  numUncompacted--) {
                 memset(out, 0, sizeof(H3Index) * numRes1);
 
diff --git a/src/h3lib/lib/algos.c b/src/h3lib/lib/algos.c
index 949988a08..1b20bf5ef 100644
--- a/src/h3lib/lib/algos.c
+++ b/src/h3lib/lib/algos.c
@@ -837,12 +837,13 @@ H3Error _getEdgeHexagons(const GeoLoop *geoloop, int64_t numHexagons, int res,
         }
         for (int64_t j = 0; j < numHexesEstimate; j++) {
             LatLng interpolate;
+            double invNumHexesEst = 1.0 / numHexesEstimate;
             interpolate.lat =
-                (origin.lat * (numHexesEstimate - j) / numHexesEstimate) +
-                (destination.lat * j / numHexesEstimate);
+                (origin.lat * (numHexesEstimate - j) * invNumHexesEst) +
+                (destination.lat * j * invNumHexesEst);
             interpolate.lng =
-                (origin.lng * (numHexesEstimate - j) / numHexesEstimate) +
-                (destination.lng * j / numHexesEstimate);
+                (origin.lng * (numHexesEstimate - j) * invNumHexesEst) +
+                (destination.lng * j * invNumHexesEst);
             H3Index pointHex;
             H3Error e = H3_EXPORT(latLngToCell)(&interpolate, res, &pointHex);
             if (e) {