diff --git a/C/eval.c b/C/eval.c
index baaeab2ca..21634f13f 100644
--- a/C/eval.c
+++ b/C/eval.c
@@ -198,6 +198,62 @@ p_is( USES_REGS1 )
   return Yap_unify_constant(ARG1,out);
 }
 
+static Int
+p_isnan( USES_REGS1 )
+{				/* X is Y	 */
+  Term out = 0L;
+  
+  while (!(out = Eval(Deref(ARG1) PASS_REGS))) {
+    if (LOCAL_Error_TYPE == RESOURCE_ERROR_STACK) {
+      LOCAL_Error_TYPE = YAP_NO_ERROR;
+      if (!Yap_gcl(LOCAL_Error_Size, 1, ENV, CP)) {
+	Yap_Error(RESOURCE_ERROR_STACK, ARG2, LOCAL_ErrorMessage);
+	return FALSE;
+      }
+    } else {
+      Yap_Error(LOCAL_Error_TYPE, LOCAL_Error_Term, LOCAL_ErrorMessage);
+      return FALSE;
+    }
+  }
+  if (IsVarTerm(out)) {
+    Yap_Error(INSTANTIATION_ERROR, out, "isnan/1");
+    return FALSE;
+  }
+  if (!IsFloatTerm(out)) {
+    Yap_Error(TYPE_ERROR_FLOAT, out, "isnan/1");
+    return FALSE;
+  }
+  return isnan(FloatOfTerm(out));
+}
+
+static Int
+p_isinf( USES_REGS1 )
+{                               /* X is Y        */
+  Term out = 0L;
+
+  while (!(out = Eval(Deref(ARG1) PASS_REGS))) {
+    if (LOCAL_Error_TYPE == RESOURCE_ERROR_STACK) {
+      LOCAL_Error_TYPE = YAP_NO_ERROR;
+      if (!Yap_gcl(LOCAL_Error_Size, 1, ENV, CP)) {
+        Yap_Error(RESOURCE_ERROR_STACK, ARG2, LOCAL_ErrorMessage);
+        return FALSE;
+      }
+    } else {
+      Yap_Error(LOCAL_Error_TYPE, LOCAL_Error_Term, LOCAL_ErrorMessage);
+      return FALSE;
+    }
+  }
+  if (IsVarTerm(out)) {
+    Yap_Error(INSTANTIATION_ERROR, out, "isinf/1");
+    return FALSE;
+  }
+  if (!IsFloatTerm(out)) {
+    Yap_Error(TYPE_ERROR_FLOAT, out, "isinf/1");
+    return FALSE;
+  }
+  return isinf(FloatOfTerm(out));
+}
+
 Int
 Yap_ArithError(yap_error_number type, Term where, char *format,...)
 {
@@ -360,6 +416,8 @@ Yap_InitEval(void)
   Yap_InitUnaryExps();
   Yap_InitBinaryExps();
   Yap_InitCPred("is", 2, p_is, 0L);
+  Yap_InitCPred("isnan", 1, p_isnan, TestPredFlag);
+  Yap_InitCPred("isinf", 1, p_isinf, TestPredFlag);
   Yap_InitCPredBack("between", 3, 2, init_between, cont_between, 0);
 }
 
diff --git a/docs/yap.tex b/docs/yap.tex
index 710ac0207..2db5b4a27 100644
--- a/docs/yap.tex
+++ b/docs/yap.tex
@@ -4458,6 +4458,20 @@ The following predicates provide counting:
 @cnindex plus/3
     True if @var{Int3} = @var{Int1} + @var{Int2}. At least two of the
     three arguments must be instantiated to integers.
+
+@item isnan(+@var{Float})
+@findex isnan/1
+@snindex isnan/1
+@cnindex isnan/1
+ True if @var{Float} is not a number.
+
+@item isinf(+@var{Float})
+@findex isinf/1
+@snindex isinf/1
+@cnindex isinf/1
+ True if floating point expression @var{Float} evaluates to infinity.
+
+
 @end table
 
 @node I/O, Database, Arithmetic, Top