diff --git a/include/valijson/constraints/concrete_constraints.hpp b/include/valijson/constraints/concrete_constraints.hpp
index 8ad29bd..9145cc3 100644
--- a/include/valijson/constraints/concrete_constraints.hpp
+++ b/include/valijson/constraints/concrete_constraints.hpp
@@ -557,7 +557,7 @@ public:
     }
 
 private:
-    size_t minItems;
+    uint64_t minItems;
 };
 
 /**
@@ -611,7 +611,7 @@ public:
     }
 
 private:
-    size_t minProperties;
+    uint64_t minProperties;
 };
 
 /**