diff --git a/ext/TensorKitChainRulesCoreExt.jl b/ext/TensorKitChainRulesCoreExt.jl
index b36976fd..0d1d0825 100644
--- a/ext/TensorKitChainRulesCoreExt.jl
+++ b/ext/TensorKitChainRulesCoreExt.jl
@@ -541,7 +541,7 @@ function qr_pullback!(ΔA::AbstractMatrix, Q::AbstractMatrix, R::AbstractMatrix,
 
     M = similar(R, (p, p))
     ΔR isa AbstractZero || mul!(M, ΔR1, R1')
-    ΔQ isa AbstractZero || mul!(M, Q1', ΔQ1, -1, +1)
+    ΔQ isa AbstractZero || mul!(M, Q1', ΔQ1, -1, !(ΔR isa AbstractZero))
     view(M, lowertriangularind(M)) .= conj.(view(M, uppertriangularind(M)))
     if eltype(M) <: Complex
         Md = view(M, diagind(M))
@@ -595,7 +595,7 @@ function lq_pullback!(ΔA::AbstractMatrix, L::AbstractMatrix, Q::AbstractMatrix,
 
     M = similar(L, (p, p))
     ΔL isa AbstractZero || mul!(M, L1', ΔL1)
-    ΔQ isa AbstractZero || mul!(M, ΔQ1, Q1', -1, +1)
+    ΔQ isa AbstractZero || mul!(M, ΔQ1, Q1', -1, !(ΔL isa AbstractZero))
     view(M, uppertriangularind(M)) .= conj.(view(M, lowertriangularind(M)))
     if eltype(M) <: Complex
         Md = view(M, diagind(M))