diff --git a/include/CPstrings.h b/include/CPstrings.h
index 711981cd..fda2f055 100644
--- a/include/CPstrings.h
+++ b/include/CPstrings.h
@@ -6,6 +6,8 @@
 #include <algorithm>
 #include <functional>
 #include <cctype>
+#include <vector>
+#include <string>
 
 #if !defined(NO_FMTLIB)
 #    ifndef FMT_HEADER_ONLY
@@ -74,17 +76,16 @@ inline bool endswith(const std::string& s1, const std::string& s2) {
 #if defined(NO_FMTLIB)
 // Missing string formatting function, this old guy is needed for ancient gcc compilers on PowerPC for VxWorks
 inline std::string format(const char* fmt, ...);
+#elif FMT_VERSION >= 50000
+template <typename... Args>
+inline std::string format(const char* format_str, const Args&... args) {
+    return fmt::sprintf(format_str, args...);
+}
 #else
-// Missing std::string formatting function - provided by the fmtlib library
 inline std::string format(const char* format, fmt::ArgList args) {
     return fmt::sprintf(format, args);
 }
 FMT_VARIADIC(std::string, format, const char*)
-// For latest FMTLIB
-/*template <typename... Args>
-    inline std::string format(const char *format_str, const Args & ... args) {
-        return fmt::sprintf(format_str, args);
-    }*/
 #endif
 
 // Missing string split - like in Python
diff --git a/include/CoolPropFluid.h b/include/CoolPropFluid.h
index 80fb9ff3..093bd294 100644
--- a/include/CoolPropFluid.h
+++ b/include/CoolPropFluid.h
@@ -562,5 +562,19 @@ class CoolPropFluid
     };
 };
 
+#if !defined(NO_FMTLIB) && FMT_VERSION >= 90000
+static int format_as(ViscosityDiluteVariables::ViscosityDiluteType type) {
+    return fmt::underlying(type);
+}
+
+static int format_as(TransportPropertyData::ViscosityHardcodedEnum viscosity) {
+    return fmt::underlying(viscosity);
+}
+
+static int format_as(TransportPropertyData::ConductivityHardcodedEnum conductivity) {
+    return fmt::underlying(conductivity);
+}
+#endif
+
 } /* namespace CoolProp */
 #endif /* COOLPROPFLUID_H_ */
diff --git a/include/DataStructures.h b/include/DataStructures.h
index 0aebc0b4..5265ac82 100644
--- a/include/DataStructures.h
+++ b/include/DataStructures.h
@@ -473,5 +473,40 @@ void extract_backend_families(std::string backend_string, backend_families& f1,
 void extract_backend_families_string(std::string backend_string, backend_families& f1, std::string& f2);
 std::string get_backend_string(backends backend);
 
+#if !defined(NO_FMTLIB) && FMT_VERSION >= 90000
+/// Allows enums to be formatted
+static int format_as(parameters parameter) {
+    return fmt::underlying(parameter);
+}
+
+static int format_as(phases phase) {
+    return fmt::underlying(phase);
+}
+
+static int format_as(schemes scheme) {
+    return fmt::underlying(scheme);
+}
+
+static int format_as(composition_types type) {
+    return fmt::underlying(type);
+}
+
+static int format_as(fluid_types type) {
+    return fmt::underlying(type);
+}
+
+static int format_as(input_pairs pair) {
+    return fmt::underlying(pair);
+}
+
+static int format_as(backend_families family) {
+    return fmt::underlying(family);
+}
+
+static int format_as(backends backend) {
+    return fmt::underlying(backend);
+}
+#endif
+
 } /* namespace CoolProp */
 #endif /* DATASTRUCTURES_H_ */
diff --git a/include/IncompressibleFluid.h b/include/IncompressibleFluid.h
index 1ea41775..b641d2e0 100644
--- a/include/IncompressibleFluid.h
+++ b/include/IncompressibleFluid.h
@@ -44,6 +44,12 @@ struct IncompressibleData
     };
 };
 
+#if !defined(NO_FMTLIB) && FMT_VERSION >= 90000
+static int format_as(IncompressibleData::IncompressibleTypeEnum type) {
+    return fmt::underlying(type);
+}
+#endif
+
 /// A property provider for incompressible solutions and pure fluids
 /**
 This fluid instance is populated using an entry from a JSON file
diff --git a/src/Backends/Helmholtz/VLERoutines.h b/src/Backends/Helmholtz/VLERoutines.h
index e13c0295..c63d0cbc 100644
--- a/src/Backends/Helmholtz/VLERoutines.h
+++ b/src/Backends/Helmholtz/VLERoutines.h
@@ -97,6 +97,12 @@ struct saturation_PHSU_pure_options
     }
 };
 
+#if !defined(NO_FMTLIB) && FMT_VERSION >= 90000
+static int format_as(saturation_PHSU_pure_options::specified_variable_options option) {
+    return fmt::underlying(option);
+}
+#endif
+
 void saturation_PHSU_pure(HelmholtzEOSMixtureBackend& HEOS, CoolPropDbl specified_value, saturation_PHSU_pure_options& options);
 
 /* \brief This is a backup saturation_p solver for the case where the Newton solver cannot approach closely enough the solution
diff --git a/src/HumidAirProp.cpp b/src/HumidAirProp.cpp
index 640bd843..eb586a63 100644
--- a/src/HumidAirProp.cpp
+++ b/src/HumidAirProp.cpp
@@ -76,6 +76,12 @@ enum givens
     GIVEN_ISENTROPIC_EXPONENT
 };
 
+#if !defined(NO_FMTLIB) && FMT_VERSION >= 90000
+int format_as(givens given) {
+    return fmt::underlying(given);
+}
+#endif
+
 void _HAPropsSI_inputs(double p, const std::vector<givens>& input_keys, const std::vector<double>& input_vals, double& T, double& psi_w);
 double _HAPropsSI_outputs(givens OuputType, double p, double T, double psi_w);
 double MoleFractionWater(double, double, int, double);