diff --git a/src/Makefile b/src/Makefile
index c56418fa2a..ead9773356 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -165,10 +165,10 @@ neat:
 # Rules
 #===============================================================================
 
-.SUFFIXES: .f90 .o
+.SUFFIXES: .F90 .o
 .PHONY: all xml-fortran clean neat distclean 
 
-%.o: %.f90
+%.o: %.F90
 	$(F90) -Ixml-fortran -Ixml-fortran/templates $(F90FLAGS) -c $<
 
 #===============================================================================
diff --git a/src/bank_header.f90 b/src/bank_header.F90
similarity index 100%
rename from src/bank_header.f90
rename to src/bank_header.F90
diff --git a/src/constants.f90 b/src/constants.F90
similarity index 100%
rename from src/constants.f90
rename to src/constants.F90
diff --git a/src/cross_section.f90 b/src/cross_section.F90
similarity index 100%
rename from src/cross_section.f90
rename to src/cross_section.F90
diff --git a/src/cross_section_header.f90 b/src/cross_section_header.F90
similarity index 100%
rename from src/cross_section_header.f90
rename to src/cross_section_header.F90
diff --git a/src/datatypes.f90 b/src/datatypes.F90
similarity index 100%
rename from src/datatypes.f90
rename to src/datatypes.F90
diff --git a/src/datatypes_header.f90 b/src/datatypes_header.F90
similarity index 100%
rename from src/datatypes_header.f90
rename to src/datatypes_header.F90
diff --git a/src/doppler.f90 b/src/doppler.F90
similarity index 100%
rename from src/doppler.f90
rename to src/doppler.F90
diff --git a/src/endf.f90 b/src/endf.F90
similarity index 100%
rename from src/endf.f90
rename to src/endf.F90
diff --git a/src/endf_header.f90 b/src/endf_header.F90
similarity index 100%
rename from src/endf_header.f90
rename to src/endf_header.F90
diff --git a/src/energy_grid.f90 b/src/energy_grid.F90
similarity index 100%
rename from src/energy_grid.f90
rename to src/energy_grid.F90
diff --git a/src/error.f90 b/src/error.F90
similarity index 100%
rename from src/error.f90
rename to src/error.F90
diff --git a/src/fileio.f90 b/src/fileio.F90
similarity index 100%
rename from src/fileio.f90
rename to src/fileio.F90
diff --git a/src/fission.f90 b/src/fission.F90
similarity index 100%
rename from src/fission.f90
rename to src/fission.F90
diff --git a/src/geometry.f90 b/src/geometry.F90
similarity index 100%
rename from src/geometry.f90
rename to src/geometry.F90
diff --git a/src/geometry_header.f90 b/src/geometry_header.F90
similarity index 100%
rename from src/geometry_header.f90
rename to src/geometry_header.F90
diff --git a/src/global.f90 b/src/global.F90
similarity index 100%
rename from src/global.f90
rename to src/global.F90
diff --git a/src/initialize.f90 b/src/initialize.F90
similarity index 100%
rename from src/initialize.f90
rename to src/initialize.F90
diff --git a/src/input_xml.f90 b/src/input_xml.F90
similarity index 100%
rename from src/input_xml.f90
rename to src/input_xml.F90
diff --git a/src/interpolation.f90 b/src/interpolation.F90
similarity index 100%
rename from src/interpolation.f90
rename to src/interpolation.F90
diff --git a/src/logging.f90 b/src/logging.F90
similarity index 100%
rename from src/logging.f90
rename to src/logging.F90
diff --git a/src/main.f90 b/src/main.F90
similarity index 100%
rename from src/main.f90
rename to src/main.F90
diff --git a/src/material_header.f90 b/src/material_header.F90
similarity index 100%
rename from src/material_header.f90
rename to src/material_header.F90
diff --git a/src/mesh.f90 b/src/mesh.F90
similarity index 100%
rename from src/mesh.f90
rename to src/mesh.F90
diff --git a/src/mesh_header.f90 b/src/mesh_header.F90
similarity index 100%
rename from src/mesh_header.f90
rename to src/mesh_header.F90
diff --git a/src/mpi_routines.f90 b/src/mpi_routines.F90
similarity index 100%
rename from src/mpi_routines.f90
rename to src/mpi_routines.F90
diff --git a/src/output.f90 b/src/output.F90
similarity index 100%
rename from src/output.f90
rename to src/output.F90
diff --git a/src/particle_header.f90 b/src/particle_header.F90
similarity index 100%
rename from src/particle_header.f90
rename to src/particle_header.F90
diff --git a/src/physics.f90 b/src/physics.F90
similarity index 100%
rename from src/physics.f90
rename to src/physics.F90
diff --git a/src/plot.f90 b/src/plot.F90
similarity index 100%
rename from src/plot.f90
rename to src/plot.F90
diff --git a/src/random_lcg.f90 b/src/random_lcg.F90
similarity index 100%
rename from src/random_lcg.f90
rename to src/random_lcg.F90
diff --git a/src/search.f90 b/src/search.F90
similarity index 100%
rename from src/search.f90
rename to src/search.F90
diff --git a/src/source.f90 b/src/source.F90
similarity index 100%
rename from src/source.f90
rename to src/source.F90
diff --git a/src/source_header.f90 b/src/source_header.F90
similarity index 100%
rename from src/source_header.f90
rename to src/source_header.F90
diff --git a/src/string.f90 b/src/string.F90
similarity index 100%
rename from src/string.f90
rename to src/string.F90
diff --git a/src/tally.f90 b/src/tally.F90
similarity index 100%
rename from src/tally.f90
rename to src/tally.F90
diff --git a/src/tally_header.f90 b/src/tally_header.F90
similarity index 100%
rename from src/tally_header.f90
rename to src/tally_header.F90
diff --git a/src/timing.f90 b/src/timing.F90
similarity index 100%
rename from src/timing.f90
rename to src/timing.F90