diff --git a/Changes b/Changes
index 4a99d0189..903cd0082 100644
--- a/Changes
+++ b/Changes
@@ -168,10 +168,10 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 * Verilator 4.020 2019-10-06
 
-***   Support $fseek, $ftell, $frewind, #1496. [Howard Su]
-
 ***   Add --public-flat-rw, #1511. [Stefan Wallentowitz]
 
+***   Support $fseek, $ftell, $frewind, #1496. [Howard Su]
+
 ***   Support vpiModule, #1469. [Stefan Wallentowitz]
 
 ****  Make Syms file honor --output-split-cfuncs, #1499. [Todd Strader]
@@ -192,6 +192,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 ****  Fix case statements with strings, #1536. [Philipp Wagner]
 
+****  Fix some coverage lost when multithreaded, #2151.
+
 
 * Verilator 4.018 2019-08-29
 
diff --git a/src/V3EmitC.cpp b/src/V3EmitC.cpp
index 0d9316a81..9352f2ab6 100644
--- a/src/V3EmitC.cpp
+++ b/src/V3EmitC.cpp
@@ -382,9 +382,15 @@ public:
         puts(");\n");
     }
     virtual void visit(AstCoverInc* nodep) VL_OVERRIDE {
-        puts("++(vlSymsp->__Vcoverage[");
-        puts(cvtToStr(nodep->declp()->dataDeclThisp()->binNum()));
-        puts("]);\n");
+        if (v3Global.opt.threads()) {
+            puts("vlSymsp->__Vcoverage[");
+            puts(cvtToStr(nodep->declp()->dataDeclThisp()->binNum()));
+            puts("].fetch_add(1, std::memory_order_relaxed);\n");
+        } else {
+            puts("++(vlSymsp->__Vcoverage[");
+            puts(cvtToStr(nodep->declp()->dataDeclThisp()->binNum()));
+            puts("]);\n");
+        }
     }
     virtual void visit(AstCReturn* nodep) VL_OVERRIDE {
         puts("return (");
@@ -1953,7 +1959,9 @@ void EmitCImp::emitCoverageDecl(AstNodeModule* modp) {
     if (v3Global.opt.coverage()) {
         ofp()->putsPrivate(true);
         putsDecoration("// Coverage\n");
-        puts("void __vlCoverInsert(uint32_t* countp, bool enable, const char* filenamep, int lineno, int column,\n");
+        puts("void __vlCoverInsert(");
+        puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+        puts("* countp, bool enable, const char* filenamep, int lineno, int column,\n");
         puts(   "const char* hierp, const char* pagep, const char* commentp);\n");
     }
 }
@@ -2068,14 +2076,22 @@ void EmitCImp::emitCoverageImp(AstNodeModule* modp) {
         puts("\n// Coverage\n");
         // Rather than putting out VL_COVER_INSERT calls directly, we do it via this function
         // This gets around gcc slowness constructing all of the template arguments.
-        puts("void " + prefixNameProtect(m_modp)
-             + "::__vlCoverInsert(uint32_t* countp, bool enable,"
-             + " const char* filenamep, int lineno, int column,\n");
+        puts("void " + prefixNameProtect(m_modp) + "::__vlCoverInsert(");
+        puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+        puts("* countp, bool enable, const char* filenamep, int lineno, int column,\n");
         puts(   "const char* hierp, const char* pagep, const char* commentp) {\n");
-        puts(   "static uint32_t fake_zero_count = 0;\n");  // static doesn't need save-restore as constant
-        puts(   "if (!enable) countp = &fake_zero_count;\n");  // Used for second++ instantiation of identical bin
-        puts(   "*countp = 0;\n");
-        puts(   "VL_COVER_INSERT(countp,");
+        if (v3Global.opt.threads()) {
+            puts(   "assert(sizeof(uint32_t) == sizeof(std::atomic<uint32_t>));\n");
+            puts(   "uint32_t* count32p = reinterpret_cast<uint32_t*>(countp);\n");
+        } else {
+            puts(   "uint32_t* count32p = countp;\n");
+        }
+        // static doesn't need save-restore as is constant
+        puts(   "static uint32_t fake_zero_count = 0;\n");
+        // Used for second++ instantiation of identical bin
+        puts(   "if (!enable) count32p = &fake_zero_count;\n");
+        puts(   "*count32p = 0;\n");
+        puts("VL_COVER_INSERT(count32p,");
         puts(   "  \"filename\",filenamep,");
         puts(   "  \"lineno\",lineno,");
         puts(   "  \"column\",column,\n");
diff --git a/src/V3EmitCSyms.cpp b/src/V3EmitCSyms.cpp
index 214fff4fd..6cdc1c635 100644
--- a/src/V3EmitCSyms.cpp
+++ b/src/V3EmitCSyms.cpp
@@ -437,7 +437,10 @@ void EmitCSyms::emitSymHdr() {
 
     if (m_coverBins) {
         puts("\n// COVERAGE\n");
-        puts("uint32_t __Vcoverage["); puts(cvtToStr(m_coverBins)); puts("];\n");
+        puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+        puts(" __Vcoverage[");
+        puts(cvtToStr(m_coverBins));
+        puts("];\n");
     }
 
     if (!m_scopeNames.empty()) {  // Scope names