diff --git a/src/PreallocationTools.jl b/src/PreallocationTools.jl
index 4440b52..a1fbcb5 100644
--- a/src/PreallocationTools.jl
+++ b/src/PreallocationTools.jl
@@ -341,6 +341,61 @@ function Base.copy(glbc::GeneralLazyBufferCache)
     new_glbc
 end
 
+# fill! dispatches for PreallocationTools types
+"""
+    fill!(dc::DiffCache, val)
+
+Fill all allocated buffers in the DiffCache with the given value.
+"""
+function Base.fill!(dc::DiffCache, val)
+    fill!(dc.du, val)
+    fill!(dc.dual_du, val)
+    fill!(dc.any_du, nothing)
+    return dc
+end
+
+"""
+    fill!(dc::FixedSizeDiffCache, val)
+
+Fill all allocated buffers in the FixedSizeDiffCache with the given value.
+"""
+function Base.fill!(dc::FixedSizeDiffCache, val)
+    fill!(dc.du, val)
+    fill!(dc.dual_du, val)
+    fill!(dc.any_du, nothing)
+    return dc
+end
+
+"""
+    fill!(lbc::LazyBufferCache, val)
+
+Fill all allocated buffers in the LazyBufferCache with the given value.
+"""
+function Base.fill!(lbc::LazyBufferCache, val)
+    for (_, buffer) in lbc.bufs
+        if buffer isa AbstractArray
+            fill!(buffer, val)
+        end
+    end
+    return lbc
+end
+
+"""
+    fill!(glbc::GeneralLazyBufferCache, val)
+
+Fill all allocated buffers in the GeneralLazyBufferCache with the given value.
+"""
+function Base.fill!(glbc::GeneralLazyBufferCache, val)
+    for (_, buffer) in glbc.bufs
+        if buffer isa AbstractArray
+            fill!(buffer, val)
+        elseif applicable(fill!, buffer, val)
+            fill!(buffer, val)
+        end
+    end
+    return glbc
+end
+
 export GeneralLazyBufferCache, FixedSizeDiffCache, DiffCache, LazyBufferCache, dualcache
 export get_tmp
 
diff --git a/test/runtests.jl b/test/runtests.jl
index c6e5e99..322eda5 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -19,7 +19,7 @@ if GROUP == "All" || GROUP == "Core"
     @safetestset "DiffCache with SparseConnectivityTracer" include("sparse_connectivity_tracer.jl")
     @safetestset "LazyBufferCache" include("lbc.jl")
     @safetestset "GeneralLazyBufferCache" include("general_lbc.jl")
-    @safetestset "Zero and Copy Dispatches" include("test_zero_copy.jl")
+    @safetestset "Zero, Copy, and Fill Dispatches" include("test_zero_copy.jl")
 end
 
 if GROUP == "GPU"
diff --git a/test/test_zero_copy.jl b/test/test_zero_copy.jl
index 9e5d20a..4a1df39 100644
--- a/test/test_zero_copy.jl
+++ b/test/test_zero_copy.jl
@@ -112,4 +112,111 @@ using Test, PreallocationTools, ForwardDiff
         copy_cache.du[1, 1] = -999
         @test cache.du[1, 1] != -999
     end
+end
+
+@testset "fill! dispatches" begin
+    @testset "DiffCache fill!" begin
+        u = rand(10)
+        cache = DiffCache(u, 5)
+        
+        # Fill with non-zero values initially
+        fill!(cache.du, 1.0)
+        fill!(cache.dual_du, 2.0)
+        push!(cache.any_du, 3.0)
+        
+        # Test fill! with 0
+        fill!(cache, 0.0)
+        @test all(cache.du .== 0)
+        @test all(cache.dual_du .== 0)
+        @test all(cache.any_du .=== nothing)
+        
+        # Test fill! with other values
+        fill!(cache, 5.0)
+        @test all(cache.du .== 5.0)
+        @test all(cache.dual_du .== 5.0)
+    end
+    
+    @testset "FixedSizeDiffCache fill!" begin
+        u = rand(10)
+        cache = FixedSizeDiffCache(u, Val{5})
+        
+        # Fill with non-zero values initially
+        fill!(cache.du, 1.0)
+        fill!(cache.dual_du, 2.0)
+        push!(cache.any_du, 3.0)
+        
+        # Test fill! with 0
+        fill!(cache, 0.0)
+        @test all(cache.du .== 0)
+        @test all(cache.dual_du .== 0)
+        @test all(cache.any_du .=== nothing)
+        
+        # Test fill! with other values
+        fill!(cache, 3.0)
+        @test all(cache.du .== 3.0)
+        @test all(cache.dual_du .== 3.0)
+    end
+    
+    @testset "LazyBufferCache fill!" begin
+        lbc = LazyBufferCache(identity)
+        u = rand(10)
+        v = rand(5, 5)
+        
+        # Create and fill buffers
+        buf1 = lbc[u]
+        fill!(buf1, 1.0)
+        buf2 = lbc[v]
+        fill!(buf2, 2.0)
+        
+        # Test fill! with 0
+        fill!(lbc, 0.0)
+        @test all(buf1 .== 0)
+        @test all(buf2 .== 0)
+        # Check that the buffers are still in the cache
+        @test lbc[u] === buf1
+        @test lbc[v] === buf2
+        
+        # Test fill! with other values
+        fill!(lbc, 7.0)
+        @test all(buf1 .== 7.0)
+        @test all(buf2 .== 7.0)
+    end
+    
+    @testset "GeneralLazyBufferCache fill!" begin
+        glbc = GeneralLazyBufferCache(u -> similar(u))
+        u = rand(10)
+        
+        # Create and fill buffer
+        buf = glbc[u]
+        fill!(buf, 1.0)
+        
+        # Test fill! with 0
+        fill!(glbc, 0.0)
+        @test all(buf .== 0)
+        # Check that the buffer is still in the cache
+        @test glbc[u] === buf
+        
+        # Test fill! with other values
+        fill!(glbc, -2.5)
+        @test all(buf .== -2.5)
+    end
+    
+    @testset "LazyBufferCache fill! with mixed types" begin
+        lbc = LazyBufferCache(identity)
+        u_float = rand(Float64, 10)
+        u_int = rand(Int, 5)
+        
+        # Create and fill buffers
+        buf_float = lbc[u_float]
+        fill!(buf_float, 1.5)
+        buf_int = lbc[u_int]
+        fill!(buf_int, 7)
+        
+        # Test fill! with 0
+        fill!(lbc, 0)
+        @test all(buf_float .== 0.0)
+        @test all(buf_int .== 0)
+        @test eltype(buf_float) == Float64
+        @test eltype(buf_int) == Int
+    end
 end
\ No newline at end of file