diff --git a/common/CMakeLists.txt b/common/CMakeLists.txt
index 6af20bf7..171cbfb4 100644
--- a/common/CMakeLists.txt
+++ b/common/CMakeLists.txt
@@ -121,6 +121,7 @@ ADD_LIBRARY(JFJochCommon STATIC
         DarkMaskSettings.h
         TopPixels.cpp
         TopPixels.h
+        hkl_key.h
 )
 
 TARGET_LINK_LIBRARIES(JFJochCommon JFJochLogger Compression JFCalibration gemmi Threads::Threads -lrt )
diff --git a/common/hkl_key.h b/common/hkl_key.h
new file mode 100644
index 00000000..fdfd4e36
--- /dev/null
+++ b/common/hkl_key.h
@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: 2024 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only
+
+# pragma once
+
+#include <cstdint>
+#include "JFJochException.h"
+
+constexpr int64_t bias = 512;
+
+inline uint64_t encode(int64_t v) {
+    const int64_t tmp = v + bias;
+    if (tmp < 0 || tmp >= 2 * bias)
+        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid, "Value out of range");
+    return static_cast<uint64_t>(tmp);
+}
+
+inline uint64_t hkl_key(const int64_t h, const int64_t k, const int64_t l) {
+    const uint64_t uh = encode(h);
+    const uint64_t uk = encode(k);
+    const uint64_t ul = encode(l);
+    return uh | (uk << 11) | (ul << 22);
+}
+
+inline int64_t decode(uint64_t v) {
+    if (v >= 2 * bias)
+        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid, "Value out of range");
+    return static_cast<int64_t>(v) - bias;
+}
+
+inline void hkl_from_key(uint64_t key, int64_t& h, int64_t& k, int64_t& l) {
+    constexpr uint64_t mask = (1ULL << 11) - 1;
+    const uint64_t uh = (key >> 0) & mask;
+    const uint64_t uk = (key >> 11) & mask;
+    const uint64_t ul = (key >> 22) & mask;
+    h = decode(uh);
+    k = decode(uk);
+    l = decode(ul);
+}
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 41156158..248d7dac 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -63,6 +63,7 @@ ADD_EXECUTABLE(jfjoch_test
         TimeTest.cpp
         RotationIndexerTest.cpp
         TopPixelsTest.cpp
+        HKLKeyTest.cpp
 )
 
 target_link_libraries(jfjoch_test Catch2WithMain JFJochBroker JFJochReceiver JFJochReader JFJochWriter JFJochImageAnalysis JFJochCommon JFJochHLSSimulation JFJochPreview)
diff --git a/tests/HKLKeyTest.cpp b/tests/HKLKeyTest.cpp
new file mode 100644
index 00000000..c147bd5e
--- /dev/null
+++ b/tests/HKLKeyTest.cpp
@@ -0,0 +1,40 @@
+// SPDX-FileCopyrightText: 2024 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only
+
+#include <catch2/catch_all.hpp>
+
+#include "../common/hkl_key.h"
+
+TEST_CASE("HKL key round-trip", "[hkl_key]") {
+    struct Case { int64_t h, k, l; };
+    const Case cases[] = {
+        {0, 0, 0},
+        {1, -2, 3},
+        {-511, 0, 511},
+        {512 - 1, -(512 - 1), 7},
+        {-128, 255, -7}
+    };
+
+    for (const auto& c : cases) {
+        const uint64_t key = hkl_key(c.h, c.k, c.l);
+        int64_t h = 0, k = 0, l = 0;
+        hkl_from_key(key, h, k, l);
+
+        CHECK(h == c.h);
+        CHECK(k == c.k);
+        CHECK(l == c.l);
+    }
+}
+
+TEST_CASE("HKL key boundaries", "[hkl_key]") {
+    const int64_t min = -512;
+    const int64_t max = 511;
+
+    const uint64_t key = hkl_key(min, 0, max);
+    int64_t h = 0, k = 0, l = 0;
+    hkl_from_key(key, h, k, l);
+
+    CHECK(h == min);
+    CHECK(k == 0);
+    CHECK(l == max);
+}
\ No newline at end of file
diff --git a/tools/XdsIntegrateParser.cpp b/tools/XdsIntegrateParser.cpp
index 7db549be..f5f7f363 100644
--- a/tools/XdsIntegrateParser.cpp
+++ b/tools/XdsIntegrateParser.cpp
@@ -8,6 +8,7 @@
 #include <stdexcept>
 
 #include "../common/ResolutionShells.h"
+#include "../common/hkl_key.h"
 
 IntegrateMap ParseXdsIntegrateHkl(const std::string& filename) {
     std::ifstream in(filename);
@@ -47,7 +48,7 @@ IntegrateMap ParseXdsIntegrateHkl(const std::string& filename) {
             entry.tail.push_back(v);
         }
 
-        result[hkl_key_16(-h, k, l)].push_back(std::move(entry));
+        result[hkl_key(-h, k, l)].push_back(std::move(entry));
     }
 
     return result;
diff --git a/tools/XdsIntegrateParser.h b/tools/XdsIntegrateParser.h
index 776e220b..ea5c19f0 100644
--- a/tools/XdsIntegrateParser.h
+++ b/tools/XdsIntegrateParser.h
@@ -12,21 +12,12 @@
 
 #include "../common/CrystalLattice.h"
 
-
 struct CcHalfByResolutionResult {
     std::vector<double> cc;
     std::vector<int32_t> pairs;
     std::vector<float> shell_mean_one_over_d2;
 };
 
-inline uint64_t hkl_key_16(int64_t h, int64_t k, int64_t l) {
-    const uint16_t bias = 512; // maps -512..512 -> 0..1024
-    uint64_t uh = static_cast<uint16_t>(std::clamp(h + bias, int64_t(0), int64_t(1024)));
-    uint64_t uk = static_cast<uint16_t>(std::clamp(k + bias, int64_t(0), int64_t(1024)));
-    uint64_t ul = static_cast<uint16_t>(std::clamp(l + bias, int64_t(0), int64_t(1024)));
-    return uh | (uk << 16) | (ul << 32);
-}
-
 struct HKLData {
     int64_t h ,k,l;
     double I = 0.0;