diff --git a/unit/TestInterface.cpp b/unit/TestInterface.cpp
index 7f708830..51fd7624 100644
--- a/unit/TestInterface.cpp
+++ b/unit/TestInterface.cpp
@@ -11,6 +11,12 @@
 #include <cmath>
 #include <cfloat>
 
+#if defined(_WIN32) || defined(__CYGWIN32__)
+// DeleteFile defined in <windows.h>
+#else
+int DeleteFile(const char* szPathName);
+#endif
+
 bool FileExists(const char *szPathName);
 VRESULT SOLUTION(double C, double Ca, double Na);
 VRESULT EQUILIBRIUM_PHASES(const char* phase, double si, double amount);