diff --git a/dlls/msvcp100/msvcp100.spec b/dlls/msvcp100/msvcp100.spec
index 39c925cd8e1..67389791bb2 100644
--- a/dlls/msvcp100/msvcp100.spec
+++ b/dlls/msvcp100/msvcp100.spec
@@ -2892,14 +2892,14 @@
 @ extern _Denorm
 @ stub _Dnorm
 @ stub _Dscale
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ extern _Eps
 @ stub _Exp
 @ stub _FCosh
 @ extern _FDenorm
 @ stub _FDnorm
 @ stub _FDscale
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ extern _FEps
 @ stub _FExp
 @ extern _FInf
@@ -2920,7 +2920,7 @@
 @ stub _LCosh
 @ extern _LDenorm
 @ stub _LDscale
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ extern _LEps
 @ stub _LExp
 @ extern _LInf
diff --git a/dlls/msvcp110/msvcp110.spec b/dlls/msvcp110/msvcp110.spec
index ff4facbd66a..f907c5b47f2 100644
--- a/dlls/msvcp110/msvcp110.spec
+++ b/dlls/msvcp110/msvcp110.spec
@@ -3745,7 +3745,7 @@
 @ cdecl _Do_call(ptr)
 @ stub _Dscale
 @ stub _Dtento
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ stub _Dunscale
 @ extern _Eps
 @ stub _Exp
@@ -3755,7 +3755,7 @@
 @ stub _FDnorm
 @ stub _FDscale
 @ stub _FDtento
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ stub _FDunscale
 @ extern _FEps
 @ stub _FExp
@@ -3791,7 +3791,7 @@
 @ stub _LDint
 @ stub _LDscale
 @ stub _LDtento
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ stub _LDunscale
 @ extern _LEps
 @ stub _LExp
diff --git a/dlls/msvcp120/msvcp120.spec b/dlls/msvcp120/msvcp120.spec
index 715703e0e6c..1f8601ccc63 100644
--- a/dlls/msvcp120/msvcp120.spec
+++ b/dlls/msvcp120/msvcp120.spec
@@ -3686,7 +3686,7 @@
 @ cdecl _Do_call(ptr)
 @ stub _Dscale
 @ stub _Dtento
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ stub _Dunscale
 @ extern _Eps
 @ stub _Exp
@@ -3696,7 +3696,7 @@
 @ stub _FDnorm
 @ stub _FDscale
 @ stub _FDtento
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ stub _FDunscale
 @ extern _FEps
 @ stub _FExp
@@ -3734,7 +3734,7 @@
 @ stub _LDint
 @ stub _LDscale
 @ stub _LDtento
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ stub _LDunscale
 @ extern _LEps
 @ stub _LExp
diff --git a/dlls/msvcp120/tests/msvcp120.c b/dlls/msvcp120/tests/msvcp120.c
index 10e03705600..9255ff1cf12 100644
--- a/dlls/msvcp120/tests/msvcp120.c
+++ b/dlls/msvcp120/tests/msvcp120.c
@@ -18,10 +18,25 @@
 
 #include <locale.h>
 #include <stdio.h>
+#include <math.h>
 
 #include "wine/test.h"
 #include "winbase.h"
 
+static inline float __port_infinity(void)
+{
+    static const unsigned __inf_bytes = 0x7f800000;
+    return *(const float *)&__inf_bytes;
+}
+#define INFINITY __port_infinity()
+
+static inline float __port_nan(void)
+{
+    static const unsigned __nan_bytes = 0x7fc00000;
+    return *(const float *)&__nan_bytes;
+}
+#define NAN __port_nan()
+
 typedef int MSVCRT_long;
 typedef unsigned char MSVCP_bool;
 
@@ -70,6 +85,7 @@ static _Cvtvec* (__cdecl *p__Getcvt)(_Cvtvec*);
 static void (CDECL *p__Call_once)(int *once, void (CDECL *func)(void));
 static void (CDECL *p__Call_onceEx)(int *once, void (CDECL *func)(void*), void *argv);
 static void (CDECL *p__Do_call)(void *this);
+static short (__cdecl *p__Dtest)(double *d);
 
 /* filesystem */
 static ULONGLONG(__cdecl *p_tr2_sys__File_size)(char const*);
@@ -119,6 +135,8 @@ static BOOL init(void)
             "_Call_onceEx");
     SET(p__Do_call,
             "_Do_call");
+    SET(p__Dtest,
+            "_Dtest");
     if(sizeof(void*) == 8) { /* 64-bit initialization */
         SET(p_tr2_sys__File_size,
                 "?_File_size@sys@tr2@std@@YA_KPEBD@Z");
@@ -407,6 +425,32 @@ static void test__Do_call(void)
     ok(cnt == 1, "func was not called\n");
 }
 
+static void test__Dtest(void)
+{
+    double d;
+    short ret;
+
+    d = 0;
+    ret = p__Dtest(&d);
+    ok(ret == FP_ZERO, "_Dtest(0) returned %x\n", ret);
+
+    d = 1;
+    ret = p__Dtest(&d);
+    ok(ret == FP_NORMAL, "_Dtest(1) returned %x\n", ret);
+
+    d = -1;
+    ret = p__Dtest(&d);
+    ok(ret == FP_NORMAL, "_Dtest(-1) returned %x\n", ret);
+
+    d = INFINITY;
+    ret = p__Dtest(&d);
+    ok(ret == FP_INFINITE, "_Dtest(INF) returned %x\n", ret);
+
+    d = NAN;
+    ret = p__Dtest(&d);
+    ok(ret == FP_NAN, "_Dtest(NAN) returned %x\n", ret);
+}
+
 static void test_tr2_sys__File_size(void)
 {
     ULONGLONG val;
@@ -910,6 +954,7 @@ START_TEST(msvcp120)
     test__Getcvt();
     test__Call_once();
     test__Do_call();
+    test__Dtest();
 
     test_tr2_sys__File_size();
     test_tr2_sys__Equivalent();
diff --git a/dlls/msvcp120_app/msvcp120_app.spec b/dlls/msvcp120_app/msvcp120_app.spec
index 1e04e7754be..b689cb913b8 100644
--- a/dlls/msvcp120_app/msvcp120_app.spec
+++ b/dlls/msvcp120_app/msvcp120_app.spec
@@ -3686,7 +3686,7 @@
 @ cdecl _Do_call(ptr) msvcp120._Do_call
 @ stub _Dscale
 @ stub _Dtento
-@ stub _Dtest
+@ cdecl _Dtest(ptr) msvcp120._Dtest
 @ stub _Dunscale
 @ extern _Eps msvcp120._Eps
 @ stub _Exp
@@ -3696,7 +3696,7 @@
 @ stub _FDnorm
 @ stub _FDscale
 @ stub _FDtento
-@ stub _FDtest
+@ cdecl _FDtest(ptr) msvcp120._FDtest
 @ stub _FDunscale
 @ extern _FEps msvcp120._FEps
 @ stub _FExp
@@ -3734,7 +3734,7 @@
 @ stub _LDint
 @ stub _LDscale
 @ stub _LDtento
-@ stub _LDtest
+@ cdecl _LDtest(ptr) msvcp120._LDtest
 @ stub _LDunscale
 @ extern _LEps msvcp120._LEps
 @ stub _LExp
diff --git a/dlls/msvcp60/msvcp60.spec b/dlls/msvcp60/msvcp60.spec
index 0aa3f1bb078..10d04e529ee 100644
--- a/dlls/msvcp60/msvcp60.spec
+++ b/dlls/msvcp60/msvcp60.spec
@@ -4258,14 +4258,14 @@
 @ extern _Denorm _Denorm
 @ stub _Dnorm
 @ stub _Dscale
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ extern _Eps _Eps
 @ stub _Exp
 @ stub _FCosh
 @ extern _FDenorm _FDenorm
 @ stub _FDnorm
 @ stub _FDscale
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ extern _FEps _FEps
 @ stub _FExp
 @ extern _FInf _FInf
@@ -4282,7 +4282,7 @@
 @ stub _LCosh
 @ extern _LDenorm _LDenorm
 @ stub _LDscale
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ extern _LEps _LEps
 @ stub _LExp
 @ extern _LInf _LInf
diff --git a/dlls/msvcp70/msvcp70.spec b/dlls/msvcp70/msvcp70.spec
index c9cdef4a0d0..f390d8a1956 100644
--- a/dlls/msvcp70/msvcp70.spec
+++ b/dlls/msvcp70/msvcp70.spec
@@ -5044,14 +5044,14 @@
 @ extern _Denorm
 @ stub _Dnorm
 @ stub _Dscale
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ extern _Eps
 @ stub _Exp
 @ stub _FCosh
 @ extern _FDenorm
 @ stub _FDnorm
 @ stub _FDscale
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ extern _FEps
 @ stub _FExp
 @ extern _FInf
@@ -5069,7 +5069,7 @@
 @ stub _LCosh
 @ extern _LDenorm
 @ stub _LDscale
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ extern _LEps
 @ stub _LExp
 @ extern _LInf
diff --git a/dlls/msvcp71/msvcp71.spec b/dlls/msvcp71/msvcp71.spec
index 2946a120796..2675c9a0be1 100644
--- a/dlls/msvcp71/msvcp71.spec
+++ b/dlls/msvcp71/msvcp71.spec
@@ -5098,14 +5098,14 @@
 @ extern _Denorm
 @ stub _Dnorm
 @ stub _Dscale
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ extern _Eps
 @ stub _Exp
 @ stub _FCosh
 @ extern _FDenorm
 @ stub _FDnorm
 @ stub _FDscale
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ extern _FEps
 @ stub _FExp
 @ extern _FInf
@@ -5125,7 +5125,7 @@
 @ stub _LCosh
 @ extern _LDenorm
 @ stub _LDscale
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ extern _LEps
 @ stub _LExp
 @ extern _LInf
diff --git a/dlls/msvcp80/msvcp80.spec b/dlls/msvcp80/msvcp80.spec
index 4e292c0dd82..ed04defa6ef 100644
--- a/dlls/msvcp80/msvcp80.spec
+++ b/dlls/msvcp80/msvcp80.spec
@@ -5705,7 +5705,7 @@
 @ stub _Dnorm
 @ stub _Dscale
 @ stub _Dtentox
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ stub _Dunscale
 @ extern _Eps
 @ stub _Exp
@@ -5714,7 +5714,7 @@
 @ stub _FDnorm
 @ stub _FDscale
 @ stub _FDtentox
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ stub _FDunscale
 @ extern _FEps
 @ stub _FExp
@@ -5736,7 +5736,7 @@
 @ extern _LDenorm
 @ stub _LDscale
 @ stub _LDtentox
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ stub _LDunscale
 @ extern _LEps
 @ stub _LExp
diff --git a/dlls/msvcp90/math.c b/dlls/msvcp90/math.c
index 439865a197f..9b827f396c8 100644
--- a/dlls/msvcp90/math.c
+++ b/dlls/msvcp90/math.c
@@ -2226,3 +2226,37 @@ complex_double* __cdecl complex_double_sqrt(complex_double *ret, const complex_d
     complex_double c = { 0.5, 0 };
     return complex_double_pow(ret, l, &c);
 }
+
+static short dclass(double x)
+{
+    switch(_fpclass(x)) {
+    case _FPCLASS_SNAN:
+    case _FPCLASS_QNAN:
+        return FP_NAN;
+    case _FPCLASS_NINF:
+    case _FPCLASS_PINF:
+        return FP_INFINITE;
+    case _FPCLASS_ND:
+    case _FPCLASS_PD:
+        return FP_SUBNORMAL;
+    case _FPCLASS_NN:
+    case _FPCLASS_PN:
+    default:
+        return FP_NORMAL;
+    case _FPCLASS_NZ:
+    case _FPCLASS_PZ:
+        return FP_ZERO;
+    }
+}
+
+/* _Dtest */
+short __cdecl _Dtest(double *x)
+{
+    return dclass(*x);
+}
+
+/* _FDtest */
+short __cdecl _FDtest(float *x)
+{
+    return dclass(*x);
+}
diff --git a/dlls/msvcp90/msvcp90.spec b/dlls/msvcp90/msvcp90.spec
index 98edb65450e..d3a314bc3ec 100644
--- a/dlls/msvcp90/msvcp90.spec
+++ b/dlls/msvcp90/msvcp90.spec
@@ -6480,14 +6480,14 @@
 @ extern _Denorm
 @ stub _Dnorm
 @ stub _Dscale
-@ stub _Dtest
+@ cdecl _Dtest(ptr)
 @ extern _Eps
 @ stub _Exp
 @ stub _FCosh
 @ extern _FDenorm
 @ stub _FDnorm
 @ stub _FDscale
-@ stub _FDtest
+@ cdecl _FDtest(ptr)
 @ extern _FEps
 @ stub _FExp
 @ extern _FInf
@@ -6507,7 +6507,7 @@
 @ stub _LCosh
 @ extern _LDenorm
 @ stub _LDscale
-@ stub _LDtest
+@ cdecl _LDtest(ptr) _Dtest
 @ extern _LEps
 @ stub _LExp
 @ extern _LInf
diff --git a/include/msvcrt/math.h b/include/msvcrt/math.h
index 34aa2685fca..c1333d4afef 100644
--- a/include/msvcrt/math.h
+++ b/include/msvcrt/math.h
@@ -146,6 +146,12 @@ static const union {
 #  endif
 #endif
 
+#define FP_INFINITE   1
+#define FP_NAN        2
+#define FP_NORMAL    -1
+#define FP_SUBNORMAL -2
+#define FP_ZERO       0
+
 #ifdef __cplusplus
 }
 #endif