diff --git a/Fortran/UnitTests/CMakeLists.txt b/Fortran/UnitTests/CMakeLists.txt
index 5c63b0da1e..9c166a644b 100644
--- a/Fortran/UnitTests/CMakeLists.txt
+++ b/Fortran/UnitTests/CMakeLists.txt
@@ -2,6 +2,7 @@
 add_subdirectory(hello)
 add_subdirectory(assign-goto)
 add_subdirectory(cray_pointers_2)
+add_subdirectory(defined_io)
 add_subdirectory(execute_command_line)
 add_subdirectory(fcvs21_f95) # NIST Fortran Compiler Validation Suite
 add_subdirectory(finalization)
diff --git a/Fortran/UnitTests/defined_io/CMakeLists.txt b/Fortran/UnitTests/defined_io/CMakeLists.txt
new file mode 100644
index 0000000000..8b9f2da57c
--- /dev/null
+++ b/Fortran/UnitTests/defined_io/CMakeLists.txt
@@ -0,0 +1,3 @@
+llvm_singlesource()
+
+file(COPY lit.local.cfg DESTINATION "${CMAKE_CURRENT_BINARY_DIR}")
diff --git a/Fortran/UnitTests/defined_io/lit.local.cfg b/Fortran/UnitTests/defined_io/lit.local.cfg
new file mode 100644
index 0000000000..1166820260
--- /dev/null
+++ b/Fortran/UnitTests/defined_io/lit.local.cfg
@@ -0,0 +1,2 @@
+config.traditional_output = True
+config.single_source = True
diff --git a/Fortran/UnitTests/defined_io/llvm-project-issue-154979.f90 b/Fortran/UnitTests/defined_io/llvm-project-issue-154979.f90
new file mode 100644
index 0000000000..115b54338d
--- /dev/null
+++ b/Fortran/UnitTests/defined_io/llvm-project-issue-154979.f90
@@ -0,0 +1,65 @@
+! A verbatim copy of test case from https://github.com/llvm/llvm-project/issues/154979
+module llvm_project_issue_154979_m
+    type base
+        real, allocatable :: data(:)
+        complex, allocatable :: cx(:)
+
+        contains
+
+        procedure :: readBaseFmtd
+        generic :: read(formatted) => readBaseFmtd
+    end type
+
+    contains
+
+    !! read in the array size before allocating dtv's components
+    subroutine readBaseFmtd (dtv, unit, iotype, v_list, iostat, iomsg)
+        class(base), intent(inout) :: dtv
+        integer, intent(in) :: unit
+        character(*), intent(in) :: iotype
+        integer, intent(in) :: v_list(:)
+        integer, intent(out) :: iostat
+        character(*), intent(inout) :: iomsg
+
+        integer isize
+
+        read (unit, *, iostat = iostat, iomsg=iomsg) isize
+        
+        if (allocated(dtv%data)) deallocate (dtv%data)
+
+        allocate (dtv%data(isize))
+
+        read (unit, *, iostat=iostat, iomsg=iomsg) dtv%data
+        read (unit, *, iostat = iostat, iomsg=iomsg) isize
+        if (allocated(dtv%cx)) deallocate (dtv%cx)
+
+        allocate (dtv%cx(isize))
+
+        read (unit, *, iostat=iostat, iomsg=iomsg) dtv%cx
+    end subroutine
+end module
+
+program llvm_project_issue_154979
+    use llvm_project_issue_154979_m
+    integer currentPos, ss
+
+    type(base) :: b1(2)
+
+
+    open (1, access='stream', form='formatted', decimal='Comma', status='scratch')
+
+    write (1, '(i4, 10(g15.7))', pos=1, decimal='Point') 10, (i*1.0, i=1, 10)
+
+    inquire (1, pos=currentPos)
+
+    write(1, *, pos=currentPos, decimal='point') 12, (cmplx(i*1.0, i*2.0), i=-12, -1)
+
+    write (1, *) 20, (i*1.22, i=1,20)
+    write (1, *, sign='plus') 22, (cmplx(i*1.1, i*2.2), i=-10,11)
+
+    allocate (b1(1)%cx(3), b1(2)%data(1000))
+    read (1, '(dp, dt, dc, dt)', pos=1) b1
+
+    print*, size(b1(1)%data)
+    print*, size(b1(1)%cx)
+end program
diff --git a/Fortran/UnitTests/defined_io/llvm-project-issue-154979.reference_output b/Fortran/UnitTests/defined_io/llvm-project-issue-154979.reference_output
new file mode 100644
index 0000000000..0e89553937
--- /dev/null
+++ b/Fortran/UnitTests/defined_io/llvm-project-issue-154979.reference_output
@@ -0,0 +1,3 @@
+ 10
+ 12
+exit 0