diff --git a/package.json b/package.json
index 6dedfc427..f28eb7cf8 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "node-sass",
   "version": "4.8.1",
-  "libsass": "3.5.0",
+  "libsass": "3.5.1",
   "description": "Wrapper around libsass",
   "license": "MIT",
   "bugs": "https://github.com/sass/node-sass/issues",
@@ -83,7 +83,7 @@
     "object-merge": "^2.5.1",
     "read-yaml": "^1.0.0",
     "rimraf": "^2.5.2",
-    "sass-spec": "^3.5.0",
+    "sass-spec": "^3.5.1",
     "unique-temp-dir": "^1.0.0"
   }
 }
diff --git a/src/libsass/docs/implementations.md b/src/libsass/docs/implementations.md
index 4321558c3..4814cdd8e 100644
--- a/src/libsass/docs/implementations.md
+++ b/src/libsass/docs/implementations.md
@@ -3,6 +3,9 @@ There are several implementations of `libsass` for a variety of languages. Here
 ### C
 * [sassc](https://github.com/hcatlin/sassc)
 
+### Crystal
+* [sass.cr](https://github.com/straight-shoota/sass.cr)
+
 ### Elixir
 * [sass.ex](https://github.com/scottdavis/sass.ex)
 
diff --git a/src/libsass/src/check_nesting.cpp b/src/libsass/src/check_nesting.cpp
index 952bb3380..19b43e0d8 100644
--- a/src/libsass/src/check_nesting.cpp
+++ b/src/libsass/src/check_nesting.cpp
@@ -108,9 +108,7 @@ namespace Sass {
     this->visit_children(i);
 
     if (Block_Ptr b = Cast<Block>(i->alternative())) {
-      for (auto n : i->alternative()->elements()) {
-        n->perform(this);
-      }
+      for (auto n : b->elements()) n->perform(this);
     }
 
     return i;
diff --git a/src/libsass/src/context.cpp b/src/libsass/src/context.cpp
index 2c51db223..b64369f63 100644
--- a/src/libsass/src/context.cpp
+++ b/src/libsass/src/context.cpp
@@ -653,8 +653,11 @@ namespace Sass {
     Expand expand(*this, &global, &backtrace);
     Cssize cssize(*this, &backtrace);
     CheckNesting check_nesting;
-    // check nesting
-    check_nesting(root);
+    // check nesting in all files
+    for (auto sheet : sheets) {
+      auto styles = sheet.second;
+      check_nesting(styles.root);
+    }
     // expand and eval the tree
     root = expand(root);
     // check nesting
diff --git a/src/libsass/src/eval.cpp b/src/libsass/src/eval.cpp
index 9ea80c05d..67fa628a3 100644
--- a/src/libsass/src/eval.cpp
+++ b/src/libsass/src/eval.cpp
@@ -1562,6 +1562,7 @@ namespace Sass {
       v->value(ops[op](lv, rn.value() * f));
     }
 
+    v->reduce();
     v->pstate(pstate);
     return v.detach();
   }
diff --git a/src/libsass/src/functions.cpp b/src/libsass/src/functions.cpp
index 8461c9096..aaa3394fb 100644
--- a/src/libsass/src/functions.cpp
+++ b/src/libsass/src/functions.cpp
@@ -102,8 +102,6 @@ namespace Sass {
 
   namespace Functions {
 
-    static Number tmpnr(ParserState("[FN]"), 0);
-
     inline void handle_utf8_error (const ParserState& pstate, Backtrace* backtrace)
     {
       try {
@@ -159,7 +157,7 @@ namespace Sass {
     {
       // Minimal error handling -- the expectation is that built-ins will be written correctly!
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val;
+      Number tmpnr(val);
       tmpnr.reduce();
       double v = tmpnr.value();
       if (!(lo <= v && v <= hi)) {
@@ -175,7 +173,7 @@ namespace Sass {
     {
       // Minimal error handling -- the expectation is that built-ins will be written correctly!
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val;
+      Number tmpnr(val);
       tmpnr.reduce();
       return tmpnr;
     }
@@ -193,7 +191,7 @@ namespace Sass {
     {
       // Minimal error handling -- the expectation is that built-ins will be written correctly!
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val;
+      Number tmpnr(val);
       tmpnr.reduce();
       /*
       if (tmpnr.unit() == "%") {
@@ -210,7 +208,7 @@ namespace Sass {
     {
       // Minimal error handling -- the expectation is that built-ins will be written correctly!
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val;
+      Number tmpnr(val);
       tmpnr.reduce();
       return tmpnr.value();
     }
@@ -218,7 +216,8 @@ namespace Sass {
     double color_num(const std::string& argname, Env& env, Signature sig, ParserState pstate, Backtrace* backtrace)
     {
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val; tmpnr.reduce();
+      Number tmpnr(val);
+      tmpnr.reduce();
       if (tmpnr.unit() == "%") {
         return std::min(std::max(tmpnr.value() * 255 / 100.0, 0.0), 255.0);
       } else {
@@ -229,7 +228,8 @@ namespace Sass {
 
     inline double alpha_num(const std::string& argname, Env& env, Signature sig, ParserState pstate, Backtrace* backtrace) {
       Number_Ptr val = get_arg<Number>(argname, env, sig, pstate, backtrace);
-      tmpnr = val; tmpnr.reduce();
+      Number tmpnr(val);
+      tmpnr.reduce();
       if (tmpnr.unit() == "%") {
         return std::min(std::max(tmpnr.value(), 0.0), 100.0);
       } else {