diff --git a/src/CFITSIO.jl b/src/CFITSIO.jl
index dbfb1f7..8a1c47b 100644
--- a/src/CFITSIO.jl
+++ b/src/CFITSIO.jl
@@ -79,6 +79,7 @@ export FITSFile,
 
 
 @enum FileMode R = 0 RW = 1
+const PREPEND_PRIMARY = -9 # copied from fitsio.h
 
 """
     cfitsio_typecode(::Type) -> Cint
@@ -1111,15 +1112,23 @@ that is capable of storing the entire array `A`.
 fits_create_img(f::FITSFile, a::AbstractArray) = fits_create_img(f, eltype(a), size(a))
 
 """
-    fits_insert_img(f::FITSFile, T::Type, naxes::Union{Vector{<:Integer}, Tuple{Vararg{Integer}}})
+    fits_insert_img(f::FITSFile, T::Type, naxes::Union{Vector{<:Integer}, Tuple{Vararg{Integer}}}[, prependprimary::Bool = false])
 
 Insert a new image extension immediately following the CHDU, or insert a new Primary Array
-at the beginning of the file.
+at the beginning of the file. A new primary image may be inserted by calling `fits_insert_img` with
+`prependprimary` set to `true` after moving to the existing primary HDU, in which case the existing
+primary HDU is converted to an image extension.
+The inserted array has an eltype `T` and size `naxes`.
+
+    fits_insert_img(f::FITSFile, a::AbstractArray{<:Real}[, prependprimary::Bool = false])
+
+Insert a new image HDU with an element type of `eltype(a)` and a size of `size(a)` that is capable
+of storing the array `a`. The flag `prependprimary` may be specified to insert a new primary image.
 """
-function fits_insert_img(f::FITSFile, T::Type, naxes::Vector{<:Integer})
+function fits_insert_img(f::FITSFile, T::Type, naxes::Vector{<:Integer}, prependprimary::Bool = false)
     fits_assert_open(f)
 
-    status = Ref{Cint}(0)
+    status = Ref{Cint}(prependprimary ? PREPEND_PRIMARY : 0)
     ccall(
         (:ffiimgll, libcfitsio),
         Cint,
@@ -1139,10 +1148,10 @@ function fits_insert_img(f::FITSFile, T::Type, naxes::Vector{<:Integer})
     fits_assert_ok(status[])
 end
 
-function fits_insert_img(f::FITSFile, T::Type, naxes::NTuple{N,Integer}) where {N}
+function fits_insert_img(f::FITSFile, T::Type, naxes::NTuple{N,Integer}, prependprimary::Bool = false) where {N}
     fits_assert_open(f)
 
-    status = Ref{Cint}(0)
+    status = Ref{Cint}(prependprimary ? PREPEND_PRIMARY : 0)
     naxesr = Ref(map(Int64, naxes))
     ccall(
         (:ffiimgll, libcfitsio),
@@ -1163,7 +1172,7 @@ function fits_insert_img(f::FITSFile, T::Type, naxes::NTuple{N,Integer}) where {
     fits_assert_ok(status[])
 end
 
-fits_insert_img(f::FITSFile, a::AbstractArray) = fits_insert_img(f, eltype(a), size(a))
+fits_insert_img(f::FITSFile, a::AbstractArray{<:Real}, prependprimary::Bool = false) = fits_insert_img(f, eltype(a), size(a), prependprimary)
 
 """
     fits_write_pix(f::FITSFile, fpixel::Union{Vector{<:Integer}, Tuple{Vararg{Integer}}}, nelements::Integer, data::StridedArray)
diff --git a/test/runtests.jl b/test/runtests.jl
index fafb2a6..4a3d52e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -280,6 +280,17 @@ end
                 fits_movabs_hdu(f, 2)
                 fits_read_pix(f, b)
                 @test b == ones(2,2) .* 4
+                # Insert new primary image
+                for sz in Any[[1,2,3], (2,4)]
+                    fits_movabs_hdu(f, 1)
+                    sz_exist = fits_get_img_size(f)
+                    fits_insert_img(f, Int, sz, true)
+                    @test fits_get_hdu_num(f) == 1
+                    @test fits_get_img_size(f) == [sz...]
+                    # test that the primary HDU is converted to an image
+                    fits_movabs_hdu(f, 2)
+                    @test fits_get_img_size(f) == sz_exist
+                end
             end
         end
     end