diff --git a/src/Transforms.c b/src/Transforms.c
index b6623bf..849c9c6 100644
--- a/src/Transforms.c
+++ b/src/Transforms.c
@@ -248,6 +248,12 @@ static int PythonFloatToOracleNumber(
     sword status;
 
     doubleValue = PyFloat_AS_DOUBLE(pythonValue);
+    if (isnan(doubleValue)) {
+        PyErr_SetString(g_DatabaseErrorException,
+                "value is not a number (NaN) and cannot be used in Oracle "
+                "numbers");
+        return -1;
+    }
     status = OCINumberFromReal(environment->errorHandle, &doubleValue,
             sizeof(double), oracleValue);
     return Environment_CheckForError(environment, status,
diff --git a/src/cx_Oracle.c b/src/cx_Oracle.c
index 7d507a7..590a9ee 100644
--- a/src/cx_Oracle.c
+++ b/src/cx_Oracle.c
@@ -18,10 +18,18 @@
 #include <datetime.h>
 #include <structmember.h>
 #include <time.h>
+#include <math.h>
 #include <oci.h>
 #include <orid.h>
 #include <xa.h>
 
+// define isnan for older versions of Visual Studio which only define _isnan
+#ifdef _WIN32
+#ifndef isnan
+#define isnan                  _isnan
+#endif
+#endif
+
 // validate OCI library
 #if !defined(OCI_MAJOR_VERSION) || (OCI_MAJOR_VERSION < 11) || \
         ((OCI_MAJOR_VERSION == 11) && (OCI_MINOR_VERSION < 2))