diff --git a/core/src/main/java/org/teavm/runtime/ExceptionHandling.java b/core/src/main/java/org/teavm/runtime/ExceptionHandling.java
index 9832660fe..4ce6bc8c7 100644
--- a/core/src/main/java/org/teavm/runtime/ExceptionHandling.java
+++ b/core/src/main/java/org/teavm/runtime/ExceptionHandling.java
@@ -99,19 +99,21 @@ public final class ExceptionHandling {
         int handlerId = 0;
         stackLoop: while (stackFrame != null) {
             int callSiteId = ShadowStack.getCallSiteId(stackFrame);
-            CallSite callSite = findCallSiteById(callSiteId, stackFrame);
-            ExceptionHandler handler = callSite.firstHandler;
+            if (callSiteId >= 0) {
+                CallSite callSite = findCallSiteById(callSiteId, stackFrame);
+                ExceptionHandler handler = callSite.firstHandler;
 
-            while (handler != null) {
-                if (handler.exceptionClass == null || handler.exceptionClass.isSupertypeOf.apply(exceptionClass)) {
-                    handlerId = handler.id;
-                    ShadowStack.setExceptionHandlerId(stackFrame, handler.id);
-                    break stackLoop;
+                while (handler != null) {
+                    if (handler.exceptionClass == null || handler.exceptionClass.isSupertypeOf.apply(exceptionClass)) {
+                        handlerId = handler.id;
+                        ShadowStack.setExceptionHandlerId(stackFrame, handler.id);
+                        break stackLoop;
+                    }
+                    handler = handler.next;
                 }
-                handler = handler.next;
-            }
 
-            ShadowStack.setExceptionHandlerId(stackFrame, callSiteId - 1);
+                ShadowStack.setExceptionHandlerId(stackFrame, callSiteId - 1);
+            }
             stackFrame = ShadowStack.getNextStackFrame(stackFrame);
         }
 
@@ -151,14 +153,16 @@ public final class ExceptionHandling {
         int size = 0;
         while (stackFrame != null) {
             int callSiteId = ShadowStack.getCallSiteId(stackFrame);
-            CallSite callSite = findCallSiteById(callSiteId, stackFrame);
-            CallSiteLocation location = callSite.location;
-            if (isObfuscated() || location == null) {
-                size++;
-            } else {
-                while (location != null) {
+            if (callSiteId >= 0) {
+                CallSite callSite = findCallSiteById(callSiteId, stackFrame);
+                CallSiteLocation location = callSite.location;
+                if (isObfuscated() || location == null) {
                     size++;
-                    location = location.next;
+                } else {
+                    while (location != null) {
+                        size++;
+                        location = location.next;
+                    }
                 }
             }
 
@@ -179,27 +183,29 @@ public final class ExceptionHandling {
         int index = 0;
         while (stackFrame != null) {
             int callSiteId = ShadowStack.getCallSiteId(stackFrame);
-            CallSite callSite = findCallSiteById(callSiteId, stackFrame);
-            CallSiteLocation location = callSite.location;
-            if (isObfuscated()) {
-                target[index++] = new StackTraceElement("Obfuscated", "obfuscated", "Obfuscated.java", callSiteId);
-            } else if (location == null) {
-                target[index++] = new StackTraceElement("", "", null, -1);
-            } else {
-                while (location != null) {
-                    MethodLocation methodLocation = location.method;
-                    StackTraceElement element;
-                    if (methodLocation != null) {
-                        element = new StackTraceElement(
-                                methodLocation.className != null ? methodLocation.className.value : "",
-                                methodLocation.methodName != null ? methodLocation.methodName.value : "",
-                                methodLocation.fileName != null ? methodLocation.fileName.value : null,
-                                location.lineNumber);
-                    } else {
-                        element = new StackTraceElement("", "", null, location.lineNumber);
+            if (callSiteId >= 0) {
+                CallSite callSite = findCallSiteById(callSiteId, stackFrame);
+                CallSiteLocation location = callSite.location;
+                if (isObfuscated()) {
+                    target[index++] = new StackTraceElement("Obfuscated", "obfuscated", "Obfuscated.java", callSiteId);
+                } else if (location == null) {
+                    target[index++] = new StackTraceElement("", "", null, -1);
+                } else {
+                    while (location != null) {
+                        MethodLocation methodLocation = location.method;
+                        StackTraceElement element;
+                        if (methodLocation != null) {
+                            element = new StackTraceElement(
+                                    methodLocation.className != null ? methodLocation.className.value : "",
+                                    methodLocation.methodName != null ? methodLocation.methodName.value : "",
+                                    methodLocation.fileName != null ? methodLocation.fileName.value : null,
+                                    location.lineNumber);
+                        } else {
+                            element = new StackTraceElement("", "", null, location.lineNumber);
+                        }
+                        target[index++] = element;
+                        location = location.next;
                     }
-                    target[index++] = element;
-                    location = location.next;
                 }
             }
             stackFrame = ShadowStack.getNextStackFrame(stackFrame);
diff --git a/core/src/main/resources/org/teavm/backend/c/string.c b/core/src/main/resources/org/teavm/backend/c/string.c
index 8e41fc0f7..4ec81f6a9 100644
--- a/core/src/main/resources/org/teavm/backend/c/string.c
+++ b/core/src/main/resources/org/teavm/backend/c/string.c
@@ -1,6 +1,12 @@
 #include "string.h"
+#include "stack.h"
 #include <stdlib.h>
 #include <string.h>
+#include <stddef.h>
+
+#if TEAVM_INCREMENTAL
+#define TEAVM_ALLOC_STACK(sz) TEAVM_ALLOC_STACK_DEF(sz, NULL)
+#endif
 
 int32_t teavm_hashCode(TeaVM_String* string) {
     int32_t hashCode = INT32_C(0);
@@ -106,9 +112,15 @@ TeaVM_String* teavm_cToString(char* cstring) {
         return NULL;
     }
 
+    TEAVM_ALLOC_STACK(1);
+    TEAVM_CALL_SITE(-1);
+    TEAVM_GC_ROOT_RELEASE(0);
+
     size_t clen = strlen(cstring);
     int32_t size = teavm_c16Size(cstring, clen);
     TeaVM_Array* charArray = teavm_allocateCharArray(size);
+    TEAVM_GC_ROOT(0, charArray);
+
     char16_t* javaChars = TEAVM_ARRAY_DATA(charArray, char16_t);
     mbstate_t state = {0};
     for (int32_t i = 0; i < size; ++i) {
@@ -120,7 +132,10 @@ TeaVM_String* teavm_cToString(char* cstring) {
             cstring += result;
         }
     }
-    return teavm_createString(charArray);
+
+    TeaVM_String* result = teavm_createString(charArray);
+    TEAVM_RELEASE_STACK;
+    return result;
 }
 
 TeaVM_String* teavm_c16ToString(char16_t* cstring) {
@@ -128,14 +143,23 @@ TeaVM_String* teavm_c16ToString(char16_t* cstring) {
         return NULL;
     }
 
+
+    TEAVM_ALLOC_STACK(1);
+    TEAVM_CALL_SITE(-1);
+    TEAVM_GC_ROOT_RELEASE(0);
+
     int32_t size = 0;
     while (cstring[size] != 0) {
         ++size;
     }
     TeaVM_Array* charArray = teavm_allocateCharArray(size);
+    TEAVM_GC_ROOT(0, charArray);
     char16_t* javaChars = TEAVM_ARRAY_DATA(charArray, char16_t);
     memcpy(javaChars, cstring, size * sizeof(char16_t));
-    return teavm_createString(charArray);
+
+    TeaVM_String* result = teavm_createString(charArray);
+    TEAVM_RELEASE_STACK;
+    return result;
 }
 
 char16_t* teavm_mbToChar16(char* cstring, int32_t* length) {