diff --git a/src/abstract_block.jl b/src/abstract_block.jl
index 6e4640f4b..95323e188 100644
--- a/src/abstract_block.jl
+++ b/src/abstract_block.jl
@@ -17,9 +17,9 @@ abstract type AbstractBlock{N} end
 
 Apply a block (of quantum circuit) to a quantum register.
 """
-@interface function apply!(r::AbstractRegister, b::AbstractBlock)
+@interface function apply!(r::AbstractRegister{B, T}, b::AbstractBlock) where {B, T}
     _check_size(r, b)
-    r.state .= mat(b) * r.state
+    r.state .= mat(T, b) * r.state
     return r
 end
 
diff --git a/src/primitive/general_matrix_gate.jl b/src/primitive/general_matrix_gate.jl
index 1488c9ddf..2ac0fd268 100644
--- a/src/primitive/general_matrix_gate.jl
+++ b/src/primitive/general_matrix_gate.jl
@@ -33,6 +33,11 @@ Create a [`GeneralMatrixBlock`](@ref) with a matrix `m`.
 julia> matblock(ComplexF64[0 1;1 0])
 matblock(...)
 ```
+
+!!!warn
+    
+    Instead of converting it to the default data type `ComplexF64`,
+    this will return its contained matrix when calling `mat`.
 """
 matblock(m::AbstractMatrix) = GeneralMatrixBlock(m)
 
@@ -43,6 +48,19 @@ Create a [`GeneralMatrixBlock`](@ref) with a matrix `m`.
 """
 matblock(m::AbstractBlock) = GeneralMatrixBlock(mat(m))
 
+"""
+    mat(A::GeneralMatrixBlock)
+
+Return the matrix of general matrix block.
+
+
+!!!warn
+    
+    Instead of converting it to the default data type `ComplexF64`,
+    this will return its contained matrix.
+"""
+mat(A::GeneralMatrixBlock) = A.mat
+
 function mat(::Type{T}, A::GeneralMatrixBlock) where T
     if eltype(A.mat) == T
         return A.mat
diff --git a/test/primitive/general_matrix_gate.jl b/test/primitive/general_matrix_gate.jl
index 03ef299a0..75bed26de 100644
--- a/test/primitive/general_matrix_gate.jl
+++ b/test/primitive/general_matrix_gate.jl
@@ -19,3 +19,7 @@ reg = rand_state(2)
 
 a = rand_unitary(2)
 @test mat(matblock(a))' == mat(matblock(a)')
+
+# fallback test #59, return a correct matrix type for matblock
+a = rand_unitary(2) .|> ComplexF32
+@test eltype(mat(matblock(a))) == ComplexF32