diff --git a/toonz/sources/common/tapptools/tcolorutils.cpp b/toonz/sources/common/tapptools/tcolorutils.cpp
index 3c5d2dc..6b3e0e7 100644
--- a/toonz/sources/common/tapptools/tcolorutils.cpp
+++ b/toonz/sources/common/tapptools/tcolorutils.cpp
@@ -14,7 +14,7 @@ typedef float KEYER_FLOAT;
 #ifdef _WIN32
 #define ISNAN _isnan
 #else
-#define ISNAN isnan
+#define ISNAN std::isnan
 #endif
 
 //------------------------------------------------------------------------------
diff --git a/toonz/sources/stdfx/pins.cpp b/toonz/sources/stdfx/pins.cpp
index b72016e..54e8df1 100644
--- a/toonz/sources/stdfx/pins.cpp
+++ b/toonz/sources/stdfx/pins.cpp
@@ -12,7 +12,7 @@
 #ifdef _WIN32
 #define ISNAN _isnan
 #else
-#define ISNAN isnan
+#define ISNAN std::isnan
 #endif
 
 namespace {