diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1997f4e0..4abeec99 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -22,17 +22,9 @@ jobs:
           - '1'
         experimental:
           - false
-        os: [ubuntu-latest]
+        os: [ubuntu-latest, windows-latest, macos-latest]
         arch: [x64]
-        include:  # spare windows/macos CI credits
-          - os: windows-latest
-            experimental: false
-            version: '1'
-            arch: x64
-          - os: macOS-latest
-            experimental: false
-            version: '1'
-            arch: x64
+        include:
           - os: ubuntu-latest
             experimental: true
             version: 'nightly'
@@ -49,12 +41,12 @@ jobs:
       - uses: julia-actions/julia-runtest@latest
         env:
           JULIA_DEBUG: 'Main,UnicodePlots'
-          COLORTERM: 'truecolor'  # 24bit
+          COLORTERM: 'truecolor' # 24bit
       - uses: julia-actions/julia-runtest@latest
         if: startsWith(matrix.os, 'ubuntu')
         env:
           JULIA_DEBUG: 'Main,UnicodePlots'
-          COLORTERM: 'yes'  # 8bit - 256 colors
+          COLORTERM: 'invalid' # 8bit - 256 colors
       - uses: julia-actions/julia-processcoverage@latest
       - uses: codecov/codecov-action@v4
         with:
diff --git a/ext/FreeTypeExt.jl b/ext/FreeTypeExt.jl
index bffa3343..b32da425 100644
--- a/ext/FreeTypeExt.jl
+++ b/ext/FreeTypeExt.jl
@@ -12,6 +12,7 @@ using FreeType
 
 const REGULAR_STYLES = "regular", "normal", "medium", "standard", "roman", "book"
 const FT_LIB = FT_Library[C_NULL]
+const LIB_LOCK = ReentrantLock()
 const VALID_FONTPATHS = String[]
 
 struct FontExtent{T}
@@ -23,16 +24,21 @@ end
 
 mutable struct FTFont
     ft_ptr::FT_Face
+    lock::ReentrantLock # lock this for the duration of any FT operation on ft_ptr
     function FTFont(ft_ptr::FT_Face)
-        face = new(ft_ptr)
-        finalizer(
-            face -> (face.ft_ptr != C_NULL && FT_LIB[1] != C_NULL) && FT_Done_Face(face),
-            face,
-        )
+        face = new(ft_ptr, ReentrantLock())
+        finalizer(safe_free, face)
         face
     end
 end
-FTFont(path::String) = FTFont(newface(path))
+
+function safe_free(face::FTFont)
+    @lock face.lock begin
+        (face.ft_ptr != C_NULL && FT_LIB[1] != C_NULL) && FT_Done_Face(face)
+    end
+end
+
+FTFont(path::String) = FTFont(new_face(path))
 FTFont(::Nothing) = nothing
 
 family_name(font::FTFont) = lowercase(ft_property(font, :family_name))
@@ -43,9 +49,9 @@ Base.propertynames(font::FTFont) = fieldnames(FT_FaceRec)
 Base.cconvert(::Type{FT_Face}, font::FTFont) = font
 Base.unsafe_convert(::Type{FT_Face}, font::FTFont) = font.ft_ptr
 
-function ft_property(font::FTFont, fieldname::Symbol)
-    fontrect = unsafe_load(font.ft_ptr)
-    if (field = getfield(fontrect, fieldname)) isa Ptr{FT_String}
+function ft_property(face::FTFont, fieldname::Symbol)
+    font_rect = @lock face.lock unsafe_load(face.ft_ptr)
+    if (field = getfield(font_rect, fieldname)) isa Ptr{FT_String}
         field == C_NULL && return ""
         unsafe_string(field)
     else
@@ -60,10 +66,10 @@ Base.show(io::IO, font::FTFont) = print(
 
 check_error(err, error_msg) = err == 0 || error("$error_msg with error: $err")
 
-function newface(facename, faceindex::Real = 0, ftlib = FT_LIB)
+function new_face(name, index::Real = 0, ftlib = FT_LIB)
     face = Ref{FT_Face}()
-    err = FT_New_Face(ftlib[1], facename, Int32(faceindex), face)
-    check_error(err, "Couldn't load font $facename")
+    err = @lock LIB_LOCK FT_New_Face(ftlib[1], name, Int32(index), face)
+    check_error(err, "Couldn't load font $name")
     face[]
 end
 
@@ -87,11 +93,12 @@ fallback_fonts() =
 const FT_FONTS = Dict{String,FTFont}()
 
 """
-Match a font using the user-specified search string. Each part of the search string
-is searched in the family name first which has to match once to include the font
-in the candidate list. For fonts with a family match the style
-name is matched next. For fonts with the same family and style name scores, regular
-fonts are preferred (any font that is "regular", "normal", "medium", "standard" or "roman")
+Match a font using the user-specified search string.
+Each part of the search string is searched in the family name first,
+which has to match once to include the font in the candidate list.
+For fonts with a family match the style name is matched next.
+For fonts with the same family and style name scores, regular fonts are preferred
+(any font that is "regular", "normal", "medium", "standard" or "roman"),
 and as a last tie-breaker, shorter overall font names are preferred.
 
 Example:
@@ -163,7 +170,7 @@ function find_font(searchstring::String; additional_fonts::String = "")
         # we can compare all four tuple elements of the score at once in order of importance:
         # 1. number of family match characters
         # 2. number of style match characters
-        # 3. is font a "regular" style variant?
+        # 3. is font a "regular" style variant ?
         # 4. the negative length of the font name, the shorter the better
         if (family_match_score = first(score)) > 0 && score > best_score
             best_fpath = fpath
@@ -201,19 +208,24 @@ FontExtent(func::Function, ext::FontExtent) = FontExtent(
 )
 
 function set_pixelsize(face::FTFont, size::Integer)
-    check_error(FT_Set_Pixel_Sizes(face, size, size), "Couldn't set pixelsize")
+    @lock face.lock check_error(
+        FT_Set_Pixel_Sizes(face, size, size),
+        "Couldn't set pixelsize",
+    )
     size
 end
 
-glyph_index(face::FTFont, glyphname::String)::UInt64 = FT_Get_Name_Index(face, glyphname)
-glyph_index(face::FTFont, char::Char)::UInt64 = FT_Get_Char_Index(face, char)
+glyph_index(face::FTFont, glyphname::String)::UInt64 =
+    @lock face.lock FT_Get_Name_Index(face, glyphname)
+glyph_index(face::FTFont, char::Char)::UInt64 =
+    @lock face.lock FT_Get_Char_Index(face, char)
 glyph_index(face::FTFont, idx::Integer) = UInt64(idx)
 
 function kerning(face::FTFont, glyphspecs...)
     i1, i2 = glyph_index.(Ref(face), glyphspecs)
     kerning2d = Ref{FT_Vector}()
-    err = FT_Get_Kerning(face, i1, i2, FT_KERNING_DEFAULT, kerning2d)
-    # can error if font has no kerning! Since that's somewhat expected, we just return 0
+    err = @lock face.lock FT_Get_Kerning(face, i1, i2, FT_KERNING_DEFAULT, kerning2d)
+    # can error if font has no kerning ! Since that's somewhat expected, we just return 0
     err == 0 || return SVector(0.0, 0.0)
     divisor = 64  # 64 since metrics are in 1/64 units (units to 26.6 fractional pixels)
     SVector(kerning2d[].x / divisor, kerning2d[].y / divisor)
@@ -221,14 +233,14 @@ end
 
 function load_glyph(face::FTFont, glyph)
     gi = glyph_index(face, glyph)
-    err = FT_Load_Glyph(face, gi, FT_LOAD_RENDER)
+    err = @lock face.lock FT_Load_Glyph(face, gi, FT_LOAD_RENDER)
     check_error(err, "Could not load glyph $(repr(glyph)) from $face to render.")
 end
 
 function load_glyph(face::FTFont, glyph, pixelsize::Integer; set_pix = true)
     set_pix && set_pixelsize(face, pixelsize)
     load_glyph(face, glyph)
-    gl = unsafe_load(ft_property(face, :glyph))
+    gl = @lock face.lock unsafe_load(ft_property(face, :glyph))
     @assert gl.format == FT_GLYPH_FORMAT_BITMAP
     gl
 end
@@ -258,7 +270,7 @@ one_or_typemax(::Type{T}) where {T<:Union{Real,Colorant}} =
 
 """
     render_string!(img::AbstractMatrix, str::String, face, pixelsize, y0, x0;
-    fcolor=one_or_typemax(T), bcolor=zero(T), halign=:hleft, valign=:vbaseline) -> Matrix
+                   fcolor=one_or_typemax(T), bcolor=zero(T), halign=:hleft, valign=:vbaseline) -> Matrix
 Render `str` into `img` using the font `face` of size `pixelsize` at coordinates `y0,x0`.
 Uses the conventions of freetype.org/freetype2/docs/glyphs/glyphs-3.html
 # Arguments
@@ -414,16 +426,22 @@ function UnicodePlots.render_string!(
 end
 
 function ft_init()
-    FT_LIB[1] != C_NULL && error("Freetype already initialized. init() called two times ?")
-    FT_Init_FreeType(FT_LIB) == 0
+    @lock LIB_LOCK begin
+        FT_LIB[1] != C_NULL &&
+            error("Freetype already initialized. init() called two times ?")
+        FT_Init_FreeType(FT_LIB) == 0
+    end
 end
 
 function ft_done()
-    FT_LIB[1] == C_NULL &&
-        error("Library == CNULL. done() called before init(), or done called two times ?")
-    err = FT_Done_FreeType(FT_LIB[1])
-    FT_LIB[1] = C_NULL
-    err == 0
+    @lock LIB_LOCK begin
+        FT_LIB[1] == C_NULL && error(
+            "Library == CNULL. done() called before init(), or done called two times ?",
+        )
+        err = FT_Done_FreeType(FT_LIB[1])
+        FT_LIB[1] = C_NULL
+        err == 0
+    end
 end
 
 add_recursive(result, path) =
@@ -441,11 +459,11 @@ function __init__()
     # so we supply a way to help it with an environment variable.
     font_paths = if Sys.isapple()  # COV_EXCL_LINE
         [
-            "/Library/Fonts", # Additional fonts that can be used by all users. This is generally where fonts go if they are to be used by other applications.
-            joinpath(homedir(), "Library/Fonts"), # Fonts specific to each user.
-            "/Network/Library/Fonts", # Fonts shared for users on a network
-            "/System/Library/Fonts", # System specific fonts
-            "/System/Library/Fonts/Supplemental", # new location since Catalina
+            "/Library/Fonts",  # additional fonts that can be used by all users: this is generally where fonts go if they are to be used by other applications
+            joinpath(homedir(), "Library/Fonts"),  # fonts specific to each user
+            "/Network/Library/Fonts",  # fonts shared for users on a network
+            "/System/Library/Fonts",  # system specific fonts
+            "/System/Library/Fonts/Supplemental",  # new location since Catalina
         ]
     elseif Sys.iswindows()  # COV_EXCL_LINE
         [
diff --git a/test/tst_freetype.jl b/test/tst_freetype.jl
index 99c52c9c..e0fd9f17 100644
--- a/test/tst_freetype.jl
+++ b/test/tst_freetype.jl
@@ -3,7 +3,8 @@ const FTE = if isdefined(Base, :get_extension)
 else
     UnicodePlots.FreeTypeExt
 end
-push!(FTE.VALID_FONTPATHS, joinpath(@__DIR__, "fonts"))
+const FT_DIR = joinpath(@__DIR__, "fonts")
+push!(FTE.VALID_FONTPATHS, FT_DIR)
 
 @testset "init and done" begin
     @test_throws ErrorException FTE.ft_init()
@@ -247,4 +248,21 @@ end
     @test FTE.fallback_fonts() isa Tuple
 end
 
+@testset "thread safety" begin
+    mktempdir() do dir
+        n = 100
+        fontfiles = map(1:n) do i
+            cp(joinpath(FT_DIR, "hack_regular.ttf"), joinpath(dir, "hack_regular_$i.ttf"))
+        end
+        Threads.@threads for f in fontfiles
+            fo = FTE.FTFont(f)
+            Threads.@threads for i = 1:n
+                FTE.load_glyph(fo, i)
+                FTE.load_glyph(fo, i, 64)
+                FTE.render_face(fo, i, 16)
+            end
+        end
+    end
+end
+
 pop!(FTE.VALID_FONTPATHS)
diff --git a/test/tst_imageplot.jl b/test/tst_imageplot.jl
index 416e3ac3..4f03961b 100644
--- a/test/tst_imageplot.jl
+++ b/test/tst_imageplot.jl
@@ -2,12 +2,13 @@ img = testimage("monarch_color_256")
 
 if !is_ci() || UnicodePlots.colormode() == 24  # FIXME: failure on ci with 8bit mode
     @testset "blocks" begin
-        _old_enc = ImageInTerminal.ENCODER_BACKEND[]
-        ImageInTerminal.ENCODER_BACKEND[] = :XTermColors
-        p = imageplot(img, title = "blocks")
-        test_ref("imageplot/img_blocks.txt", @show_col(p, :displaysize => T_SZ))
-        @test !p.graphics.sixel[]
-        ImageInTerminal.ENCODER_BACKEND[] = _old_enc
+        let _old_enc = ImageInTerminal.ENCODER_BACKEND[]
+            ImageInTerminal.ENCODER_BACKEND[] = :XTermColors
+            p = imageplot(img, title = "blocks")
+            test_ref("imageplot/img_blocks.txt", @show_col(p, :displaysize => T_SZ))
+            @test !p.graphics.sixel[]
+            ImageInTerminal.ENCODER_BACKEND[] = _old_enc
+        end
     end
 end
 
@@ -15,11 +16,12 @@ end
 # must be launched with `Pkg.test("UnicodePlots"; forward_stdin=true)` on `1.8`+
 if !is_ci() && ImageInTerminal.Sixel.is_sixel_supported()
     @testset "sixel" begin
-        _old_enc = ImageInTerminal.ENCODER_BACKEND[]
-        ImageInTerminal.ENCODER_BACKEND[] = :Sixel
-        p = imageplot(img, title = "sixel")
-        test_ref("imageplot/img_sixel.txt", @show_col(p, :displaysize => T_SZ))
-        @test p.graphics.sixel[]
-        ImageInTerminal.ENCODER_BACKEND[] = _old_enc
+        let _old_enc = ImageInTerminal.ENCODER_BACKEND[]
+            ImageInTerminal.ENCODER_BACKEND[] = :Sixel
+            p = imageplot(img, title = "sixel")
+            test_ref("imageplot/img_sixel.txt", @show_col(p, :displaysize => T_SZ))
+            @test p.graphics.sixel[]
+            ImageInTerminal.ENCODER_BACKEND[] = _old_enc
+        end
     end
 end