diff --git a/src/gray_params.f90 b/src/gray_params.f90
index 140b85f..f1b78f0 100644
--- a/src/gray_params.f90
+++ b/src/gray_params.f90
@@ -344,13 +344,16 @@ contains
     close(u)
 
     ! Convert all filenames to absolute paths
-    ! Note: `filenm` is assumed to be a path relative to the
-    ! gray_params.data file.
     block
-      use utils, only : dirname
-      params%antenna%filenm     = dirname(filename) // params%antenna%filenm
-      params%equilibrium%filenm = dirname(filename) // params%equilibrium%filenm
-      params%profiles%filenm    = dirname(filename) // params%profiles%filenm
+      use utils, only : dirname, isrelative
+      if (isrelative(params%antenna%filenm))     &
+        params%antenna%filenm     = dirname(filename) // params%antenna%filenm
+
+      if (isrelative(params%equilibrium%filenm)) &
+        params%equilibrium%filenm = dirname(filename) // params%equilibrium%filenm
+
+      if (isrelative(params%profiles%filenm))    &
+        params%profiles%filenm    = dirname(filename) // params%profiles%filenm
     end block
   end subroutine read_parameters
 
diff --git a/src/utils.f90 b/src/utils.f90
index 7a93f93..a2cc142 100644
--- a/src/utils.f90
+++ b/src/utils.f90
@@ -293,10 +293,20 @@ contains
     directory = filepath(1:last_sep)
 
     ! append the cwd to relative paths
-    if (filepath(1:1) /= '/') then
+    if (isrelative(filepath)) then
       call getcwd(cwd)
       directory = trim(cwd) // '/' // directory
     end if
   end function dirname
 
+  function isrelative(filepath)
+    ! Check if `filepath` is a relative or an absolute path
+
+    ! function arguments
+    character(*), intent(in)  :: filepath
+    logical :: isrelative
+
+    isrelative = (filepath(1:1) /= '/')
+  end function isrelative
+
 end module utils