diff --git a/src/MNH/gamma_inc.f90 b/src/MNH/gamma_inc.f90
index 083bf6d471c7f9c91a0a537dc172b05491bfb3c6..93e6247d062f1142e4365d64204aeac782c73a6c 100644
--- a/src/MNH/gamma_inc.f90
+++ b/src/MNH/gamma_inc.f90
@@ -87,7 +87,7 @@ REAL                                 :: ZFPMIN=1.E-30
 REAL                                 :: ZAP,ZDEL,ZSUM
 REAL                                 :: ZAN,ZB,ZC,ZD,ZH
 !
-IF( PX<0.0 .OR. PA>=0.0 ) call Print_msg(NVERB_FATAL,'GEN','GAMMA_INC','invalid arguments: PX<0.0 .OR. PA>=0.0')
+IF( PX<0.0 .OR. PA<=0.0 ) call Print_msg(NVERB_FATAL,'GEN','GAMMA_INC','invalid arguments: PX<0.0 .OR. PA<=0.0')
 !
 IF( (PX.LT.PA+1.0) ) THEN
   ZAP = PA
diff --git a/src/MNH/gamma_inc_low.f90 b/src/MNH/gamma_inc_low.f90
index dabcd722af43a6ee05c802adef69fb45dab2b112..bec06e6f00d3130d0a29f5f4a673c995fd5934a1 100644
--- a/src/MNH/gamma_inc_low.f90
+++ b/src/MNH/gamma_inc_low.f90
@@ -109,7 +109,7 @@ ZS(5) = 2.9092306039
 !
 !*       1 Compute coefficients
 !
-IF( PX<0.0 .OR. PA>=0.0 ) call Print_msg(NVERB_FATAL,'GEN','GAMMA_INC_LOW','invalid arguments: PX<0.0 .OR. PA>=0.0')
+IF( PX<0.0 .OR. PA<=0.0 ) call Print_msg(NVERB_FATAL,'GEN','GAMMA_INC_LOW','invalid arguments: PX<0.0 .OR. PA<=0.0')
 !
 ZC(1) = 1.+ZP(1)*PA+ZP(2)*PA**2+ZP(3)*PA**3+ZP(4)*PA**4+ZP(5)*(EXP(-ZP(6)*PA)-1)
 !