diff --git a/src/sfizz/modulations/ModKey.cpp b/src/sfizz/modulations/ModKey.cpp
index 61b55859f..af38defda 100644
--- a/src/sfizz/modulations/ModKey.cpp
+++ b/src/sfizz/modulations/ModKey.cpp
@@ -228,7 +228,7 @@ std::string ModKey::toString() const
     }
 }
 
-ModKey ModKey::getSourceDepthKey(ModKey source, ModKey target)
+ModKey ModKey::getSourceDepthKey(const ModKey& source, const ModKey& target)
 {
     const NumericId<Region> region = source.region();
     const ModKey::Parameters& tp = target.parameters();
diff --git a/src/sfizz/modulations/ModKey.h b/src/sfizz/modulations/ModKey.h
index 92f11ca43..b3047eba7 100644
--- a/src/sfizz/modulations/ModKey.h
+++ b/src/sfizz/modulations/ModKey.h
@@ -26,7 +26,10 @@ class ModKey {
 
     ModKey() = default;
     explicit ModKey(ModId id, NumericId<Region> region = {}, Parameters params = {})
-        : id_(id), region_(region), params_(params), flags_(ModIds::flags(id_)) {}
+        : id_(id), region_(region), params_(params), flags_(ModIds::flags(id_))
+        {
+            calculateHash();
+        }
 
     static ModKey createCC(uint16_t cc, uint8_t curve, uint16_t smooth, float step);
     static ModKey createNXYZ(ModId id, NumericId<Region> region = {}, uint8_t N = 0, uint8_t X = 0, uint8_t Y = 0, uint8_t Z = 0);
@@ -46,7 +49,7 @@ class ModKey {
      * @brief Obtain the modulation key of the source depth, in the connection
      * between source and target, if such a key exists.
      */
-    static ModKey getSourceDepthKey(ModKey source, ModKey target);
+    static ModKey getSourceDepthKey(const ModKey& source, const ModKey& target);
 
     struct RawParameters {
         union {
@@ -94,6 +97,10 @@ class ModKey {
         return !this->operator==(other);
     }
 
+public:
+    size_t hash() const { return hash_; };
+private:
+    void calculateHash();
 
 private:
     //! Identifier
@@ -104,6 +111,9 @@ class ModKey {
     Parameters params_ {};
     // Memorize the flag
     int flags_;
+    // Hash number
+    size_t hash_ = size_t(16806506973555142816ULL);
 };
 
+
 } // namespace sfz
diff --git a/src/sfizz/modulations/ModKeyHash.cpp b/src/sfizz/modulations/ModKeyHash.cpp
index a8b8ac6f0..f51d36d59 100644
--- a/src/sfizz/modulations/ModKeyHash.cpp
+++ b/src/sfizz/modulations/ModKeyHash.cpp
@@ -10,12 +10,27 @@
 #include "utility/StringViewHelpers.h"
 #include <cstdint>
 
-size_t std::hash<sfz::ModKey>::operator()(const sfz::ModKey &key) const
+void sfz::ModKey::calculateHash()
 {
-    uint64_t k = hashNumber(static_cast<int>(key.id()));
-    const sfz::ModKey::Parameters& p = key.parameters();
+#if !defined(NDEBUG)
+    static bool once = false;
+    if (!once) {
+        once = true;
+        ModKey m;
+        size_t h = m.hash();
+        m.calculateHash();
+        if (h != m.hash()) {
+            printf("ModKey default hash is %llu\n", (uint64_t)m.hash());
+            assert(false && "Number of variables is wrong. Needs updating the default hash.");
+        }
+    }
+#endif
 
-    switch (key.id()) {
+    uint64_t k = hashNumber(static_cast<int>(id()));
+    k = hashNumber(region_.number(), k);
+    const sfz::ModKey::Parameters& p = parameters();
+
+    switch (id()) {
     case sfz::ModId::Controller:
         k = hashNumber(p.cc, k);
         k = hashNumber(p.curve, k);
@@ -29,5 +44,10 @@ size_t std::hash<sfz::ModKey>::operator()(const sfz::ModKey &key) const
         k = hashNumber(p.Z, k);
         break;
     }
-    return k;
+    hash_ = size_t(k);
+}
+
+size_t std::hash<sfz::ModKey>::operator()(const sfz::ModKey &key) const
+{
+    return key.hash();
 }
diff --git a/src/sfizz/utility/StringViewHelpers.h b/src/sfizz/utility/StringViewHelpers.h
index 278833c18..9fcf355da 100644
--- a/src/sfizz/utility/StringViewHelpers.h
+++ b/src/sfizz/utility/StringViewHelpers.h
@@ -101,7 +101,12 @@ uint64_t hashNumber(Int i, uint64_t h = Fnv1aBasis)
 {
     static_assert(std::is_arithmetic<Int>::value,
                   "The hashed object must be of arithmetic type");
-    return hash(absl::string_view(reinterpret_cast<const char*>(&i), sizeof(i)), h);
+    union {
+        uint64_t u64;
+        Int i;
+    } un {};
+    un.i = i;
+    return (h ^ un.u64) * Fnv1aPrime;
 }
 
 /**