diff --git a/src/gray_params.f90 b/src/gray_params.f90
index 0cdf4c3..6c06a84 100644
--- a/src/gray_params.f90
+++ b/src/gray_params.f90
@@ -203,6 +203,25 @@ module gray_params
     type(misc_parameters)        :: misc
   end type
 
+  ! List of mandatory GRAY parameters
+  integer, parameter :: max_name_size = 40
+  character(len=*), parameter :: mandatory(*) = [ &
+    character(len=max_name_size) :: &
+    "antenna.alpha",                &
+    "antenna.beta",                 &
+    "antenna.iox",                  &
+    "antenna.ibeam",                &
+    "antenna.filenm",               &
+    "equilibrium.filenm",           &
+    "profiles.irho",                &
+    "profiles.iprof",               &
+    "profiles.filenm",              &
+    "raytracing.dst",               &
+    "raytracing.nrayr",             &
+    "raytracing.nrayth",            &
+    "misc.rwall"                    &
+  ]
+
   ! All GRAY input data
   type gray_data
     type(equilibrium_data) :: equilibrium
@@ -355,15 +374,31 @@ contains
 
   subroutine read_gray_config(filename, params, err)
     ! Reads the GRAY parameters from the gray.ini configuration file
-    use ini_parser, only : parse_ini, property_handler, ini_error
-
+    use ini_parser, only : parse_ini, property_handler, ini_error, ERR_SUCCESS
+    use logger,     only : log_error
 
     ! subroutine arguments
     character(len=*),         intent(in)  :: filename
     type(gray_parameters),    intent(out) :: params
     integer(kind(ini_error)), intent(out) :: err
 
+    integer, parameter :: max_lines = 100
+    integer :: count, i
+    character(len=max_name_size) :: provided(max_lines), name
+
+    ! parse the configuration
+    count = 1
     call parse_ini(filename, ini_handler, err)
+    if (err /= ERR_SUCCESS) return
+
+    ! check if all mandatory parameters were given
+    do i = 1, size(mandatory)
+      name = mandatory(i)
+      if (findloc(provided, trim(name), count) /= 0) cycle
+      call log_error('mandatory parameter `'//trim(name)//'` is missing!', &
+                     mod='gray_params', proc='read_gray_config')
+      err = 1
+    end do
 
     contains
 
@@ -376,6 +411,10 @@ contains
         integer(kind(ini_error)) :: err
 
         err = update_parameter(params, section // "." // name, value)
+
+        ! store the parameter name
+        provided(count) = section // "." // name
+        count = count + 1
       end function ini_handler
 
   end subroutine read_gray_config
diff --git a/src/ini_parser.f90 b/src/ini_parser.f90
index 886c3e4..7461a6f 100644
--- a/src/ini_parser.f90
+++ b/src/ini_parser.f90
@@ -137,7 +137,7 @@ contains
           cycle
 
         case (ERR_VALUE)
-          write (msg, '("invalid value for property ",a,": ", a)') name, value
+          write (msg, '("invalid value for property `",a,"`: ", a)') name, value
           call log_error(msg, proc='parse_ini', mod='ini_parser')
           deallocate(line)
           error = ERR_VALUE