diff --git a/src/gausskronrod.jl b/src/gausskronrod.jl
index 7c09e9a..c2042f3 100644
--- a/src/gausskronrod.jl
+++ b/src/gausskronrod.jl
@@ -598,13 +598,20 @@ const wgd7 = [1.2948496616886969327061143267787e-01,
 const rulecache = Dict{Type,Dict}(
     Float64 => Dict{Int,NTuple{3,Vector{Float64}}}(7 => (xd7,wd7,wgd7)),
     Float32 => Dict{Int,NTuple{3,Vector{Float32}}}(7 => (xd7,wd7,wgd7)))
+const rulecache_lock = ReentrantLock() # thread-safety
 
 # for BigFloat rules, we need a separate cache keyed by (n,precision)
 const bigrulecache = Dict{Tuple{Int,Int}, NTuple{3,Vector{BigFloat}}}()
+const bigrulecache_lock = ReentrantLock() # thread-safety
 
 function cachedrule(::Union{Type{BigFloat},Type{Complex{BigFloat}}}, n::Integer)
     key = (Int(n), precision(BigFloat))
-    haskey(bigrulecache, key) ? bigrulecache[key] : (bigrulecache[key] = kronrod(BigFloat, Int(n)))
+    lock(bigrulecache_lock)
+    try
+        return haskey(bigrulecache, key) ? bigrulecache[key] : (bigrulecache[key] = kronrod(BigFloat, Int(n)))
+    finally
+        unlock(bigrulecache_lock)
+    end
 end
 
 # use a generated function to make this type-stable
@@ -613,5 +620,22 @@ end
     :(haskey($cache, n) ? $cache[n] : ($cache[n] = kronrod($TF, n)))
 end
 
-cachedrule(::Type{T}, n::Integer) where {T<:Number} =
-    _cachedrule(typeof(float(real(one(T)))), Int(n))
+function cachedrule(::Type{T}, n::Integer) where {T<:Number}
+    lock(rulecache_lock)
+    try
+        return _cachedrule(typeof(float(real(one(T)))), Int(n))
+    finally
+        unlock(rulecache_lock)
+    end
+end
+
+# fast path for common case of Float64 precision and default order
+function cachedrule(::Union{Type{Float64},Type{ComplexF64}}, n::Integer)
+    n == 7 && return (xd7,wd7,wgd7)
+    lock(rulecache_lock)
+    try
+        return _cachedrule(Float64, Int(n))
+    finally
+        unlock(rulecache_lock)
+    end
+end