diff --git a/CMakeLists.txt b/CMakeLists.txt
index 83f8ac5f8..32c8075cf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -178,7 +178,6 @@ add_library(FV3::fv3 ALIAS fv3)
 
 set_property(SOURCE model/nh_utils.F90 APPEND_STRING PROPERTY COMPILE_FLAGS "${FAST}")
 set_property(SOURCE model/fv_mapz.F90  APPEND_STRING PROPERTY COMPILE_FLAGS "${FAST}")
-set_property(SOURCE tools/fv_diagnostics.F90  APPEND_STRING PROPERTY COMPILE_FLAGS "-O0")
 
 set_target_properties(fv3 PROPERTIES Fortran_MODULE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include/fv3)
 target_include_directories(fv3 PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/include/fv3>
diff --git a/tools/fv_diagnostics.F90 b/tools/fv_diagnostics.F90
index 9eb883a8e..cc6f846e5 100644
--- a/tools/fv_diagnostics.F90
+++ b/tools/fv_diagnostics.F90
@@ -4270,20 +4270,9 @@ subroutine range_check_3d(qname, q, is, ie, js, je, n_g, km, pos, q_low, q_hi, b
       integer year, month, day, hour, minute, second
 
       if ( present(bad_range) ) bad_range = .false.
-      qmin = q(is,js,1)
-      qmax = qmin
 
-      do k=1,km
-      do j=js,je
-         do i=is,ie
-            if( q(i,j,k) < qmin ) then
-                qmin = q(i,j,k)
-            elseif( q(i,j,k) > qmax ) then
-                qmax = q(i,j,k)
-            endif
-          enddo
-      enddo
-      enddo
+      qmin=minval(q(is:ie,js:je,1:km))
+      qmax=maxval(q(is:ie,js:je,1:km))
 
       call mp_reduce_min(qmin)
       call mp_reduce_max(qmax)
@@ -4337,18 +4326,9 @@ subroutine range_check_2d(qname, q, is, ie, js, je, n_g, pos, q_low, q_hi, bad_r
       integer year, month, day, hour, minute, second
 
       if ( present(bad_range) ) bad_range = .false.
-      qmin = q(is,js)
-      qmax = qmin
 
-      do j=js,je
-         do i=is,ie
-            if( q(i,j) < qmin ) then
-                qmin = q(i,j)
-            elseif( q(i,j) > qmax ) then
-                qmax = q(i,j)
-            endif
-          enddo
-      enddo
+      qmin=minval(q(is:ie,js:je))
+      qmax=maxval(q(is:ie,js:je))
 
       call mp_reduce_min(qmin)
       call mp_reduce_max(qmax)