diff --git a/src/detect-engine.c b/src/detect-engine.c
index 9cfb222dd421..f1c47b0fa356 100644
--- a/src/detect-engine.c
+++ b/src/detect-engine.c
@@ -1653,11 +1653,13 @@ void InspectionBufferFree(InspectionBuffer *buffer)
 /**
  * \brief make sure that the buffer has at least 'min_size' bytes
  * Expand the buffer if necessary
+ *
+ * \retval pointer to inner buffer to use, or NULL if realloc failed
  */
-void InspectionBufferCheckAndExpand(InspectionBuffer *buffer, uint32_t min_size)
+uint8_t *InspectionBufferCheckAndExpand(InspectionBuffer *buffer, uint32_t min_size)
 {
     if (likely(buffer->size >= min_size))
-        return;
+        return buffer->buf;
 
     uint32_t new_size = (buffer->size == 0) ? 4096 : buffer->size;
     while (new_size < min_size) {
@@ -1668,7 +1670,24 @@ void InspectionBufferCheckAndExpand(InspectionBuffer *buffer, uint32_t min_size)
     if (ptr != NULL) {
         buffer->buf = ptr;
         buffer->size = new_size;
+    } else {
+        return NULL;
     }
+    return buffer->buf;
+}
+
+/**
+ * \brief set inspect length of inspect buffer
+ * The inspect buffer may have been overallocated (by strip_whitespace for example)
+ * so, this sets the final length
+ */
+void InspectionBufferTruncate(InspectionBuffer *buffer, uint32_t buf_len)
+{
+    DEBUG_VALIDATE_BUG_ON(buffer->buf == NULL);
+    DEBUG_VALIDATE_BUG_ON(buf_len > buffer->size);
+    buffer->inspect = buffer->buf;
+    buffer->inspect_len = buf_len;
+    buffer->initialized = true;
 }
 
 void InspectionBufferCopy(InspectionBuffer *buffer, uint8_t *buf, uint32_t buf_len)
diff --git a/src/detect-engine.h b/src/detect-engine.h
index a1732b16a993..006aff972aa5 100644
--- a/src/detect-engine.h
+++ b/src/detect-engine.h
@@ -31,7 +31,8 @@ void InspectionBufferInit(InspectionBuffer *buffer, uint32_t initial_size);
 void InspectionBufferSetup(DetectEngineThreadCtx *det_ctx, const int list_id,
         InspectionBuffer *buffer, const uint8_t *data, const uint32_t data_len);
 void InspectionBufferFree(InspectionBuffer *buffer);
-void InspectionBufferCheckAndExpand(InspectionBuffer *buffer, uint32_t min_size);
+uint8_t *InspectionBufferCheckAndExpand(InspectionBuffer *buffer, uint32_t min_size);
+void InspectionBufferTruncate(InspectionBuffer *buffer, uint32_t buf_len);
 void InspectionBufferCopy(InspectionBuffer *buffer, uint8_t *buf, uint32_t buf_len);
 void InspectionBufferApplyTransforms(InspectionBuffer *buffer,
         const DetectEngineTransforms *transforms);
diff --git a/src/detect-transform-casechange.c b/src/detect-transform-casechange.c
index 851030828ced..f22667033612 100644
--- a/src/detect-transform-casechange.c
+++ b/src/detect-transform-casechange.c
@@ -62,12 +62,15 @@ static void DetectTransformToLower(InspectionBuffer *buffer, void *options)
         return;
     }
 
-    uint8_t output[input_len];
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
     for (uint32_t i = 0; i < input_len; i++) {
         output[i] = u8_tolower(input[i]);
     }
 
-    InspectionBufferCopy(buffer, output, input_len);
+    InspectionBufferTruncate(buffer, input_len);
 }
 /**
  *  \internal
@@ -102,12 +105,15 @@ static void DetectTransformToUpper(InspectionBuffer *buffer, void *options)
         return;
     }
 
-    uint8_t output[input_len];
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
     for (uint32_t i = 0; i < input_len; i++) {
         output[i] = u8_toupper(input[i]);
     }
 
-    InspectionBufferCopy(buffer, output, input_len);
+    InspectionBufferTruncate(buffer, input_len);
 }
 
 /*
diff --git a/src/detect-transform-compress-whitespace.c b/src/detect-transform-compress-whitespace.c
index 5cbf0fd896f5..cc78c7e62281 100644
--- a/src/detect-transform-compress-whitespace.c
+++ b/src/detect-transform-compress-whitespace.c
@@ -111,7 +111,11 @@ static void TransformCompressWhitespace(InspectionBuffer *buffer, void *options)
         return;
     }
 
-    uint8_t output[input_len]; // we can only shrink
+    // we can only shrink
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
     uint8_t *oi = output, *os = output;
 
     //PrintRawDataFp(stdout, input, input_len);
@@ -132,7 +136,7 @@ static void TransformCompressWhitespace(InspectionBuffer *buffer, void *options)
     uint32_t output_size = oi - os;
     //PrintRawDataFp(stdout, output, output_size);
 
-    InspectionBufferCopy(buffer, os, output_size);
+    InspectionBufferTruncate(buffer, output_size);
 }
 
 #ifdef UNITTESTS
diff --git a/src/detect-transform-dotprefix.c b/src/detect-transform-dotprefix.c
index 52a263372b43..295a149f8941 100644
--- a/src/detect-transform-dotprefix.c
+++ b/src/detect-transform-dotprefix.c
@@ -110,11 +110,15 @@ static void TransformDotPrefix(InspectionBuffer *buffer, void *options)
     const size_t input_len = buffer->inspect_len;
 
     if (input_len) {
-        uint8_t output[input_len + 1]; // For the leading '.'
+        // For the leading '.'
+        uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len + 1);
+        if (output == NULL) {
+            return;
+        }
 
         output[0] = '.';
         memcpy(&output[1], buffer->inspect, input_len);
-        InspectionBufferCopy(buffer, output, input_len + 1);
+        InspectionBufferTruncate(buffer, input_len + 1);
     }
 }
 
diff --git a/src/detect-transform-header-lowercase.c b/src/detect-transform-header-lowercase.c
index 7c776201b308..b04ded3a68ba 100644
--- a/src/detect-transform-header-lowercase.c
+++ b/src/detect-transform-header-lowercase.c
@@ -53,7 +53,10 @@ static void DetectTransformHeaderLowercase(InspectionBuffer *buffer, void *optio
     if (input_len == 0) {
         return;
     }
-    uint8_t output[input_len];
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
 
     // state 0 is header name, 1 is header value
     int state = 0;
@@ -72,7 +75,7 @@ static void DetectTransformHeaderLowercase(InspectionBuffer *buffer, void *optio
             }
         }
     }
-    InspectionBufferCopy(buffer, output, input_len);
+    InspectionBufferTruncate(buffer, input_len);
 }
 
 void DetectTransformHeaderLowercaseRegister(void)
diff --git a/src/detect-transform-strip-pseudo-headers.c b/src/detect-transform-strip-pseudo-headers.c
index 450900d46037..d755d5fa45a5 100644
--- a/src/detect-transform-strip-pseudo-headers.c
+++ b/src/detect-transform-strip-pseudo-headers.c
@@ -53,7 +53,10 @@ static void DetectTransformStripPseudoHeaders(InspectionBuffer *buffer, void *op
     if (input_len == 0) {
         return;
     }
-    uint8_t output[input_len];
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
 
     bool new_line = true;
     bool pseudo = false;
@@ -82,7 +85,7 @@ static void DetectTransformStripPseudoHeaders(InspectionBuffer *buffer, void *op
             j++;
         }
     }
-    InspectionBufferCopy(buffer, output, j);
+    InspectionBufferTruncate(buffer, j);
 }
 
 void DetectTransformStripPseudoHeadersRegister(void)
diff --git a/src/detect-transform-strip-whitespace.c b/src/detect-transform-strip-whitespace.c
index 32fb96f06ea0..60405927a1de 100644
--- a/src/detect-transform-strip-whitespace.c
+++ b/src/detect-transform-strip-whitespace.c
@@ -106,7 +106,11 @@ static void TransformStripWhitespace(InspectionBuffer *buffer, void *options)
     if (input_len == 0) {
         return;
     }
-    uint8_t output[input_len]; // we can only shrink
+    // we can only shrink
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
     uint8_t *oi = output, *os = output;
 
     //PrintRawDataFp(stdout, input, input_len);
@@ -119,7 +123,7 @@ static void TransformStripWhitespace(InspectionBuffer *buffer, void *options)
     uint32_t output_size = oi - os;
     //PrintRawDataFp(stdout, output, output_size);
 
-    InspectionBufferCopy(buffer, os, output_size);
+    InspectionBufferTruncate(buffer, output_size);
 }
 
 #ifdef UNITTESTS
diff --git a/src/detect-transform-urldecode.c b/src/detect-transform-urldecode.c
index 13ef03372f5f..a4e9655ad7e9 100644
--- a/src/detect-transform-urldecode.c
+++ b/src/detect-transform-urldecode.c
@@ -125,12 +125,16 @@ static void TransformUrlDecode(InspectionBuffer *buffer, void *options)
     if (input_len == 0) {
         return;
     }
-    uint8_t output[input_len]; // we can only shrink
+    // we can only shrink
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
 
     changed = BufferUrlDecode(input, input_len, output, &output_size);
 
     if (changed) {
-        InspectionBufferCopy(buffer, output, output_size);
+        InspectionBufferTruncate(buffer, output_size);
     }
 }
 
diff --git a/src/detect-transform-xor.c b/src/detect-transform-xor.c
index e42700feb369..18f96df3cf46 100644
--- a/src/detect-transform-xor.c
+++ b/src/detect-transform-xor.c
@@ -133,12 +133,15 @@ static void DetectTransformXor(InspectionBuffer *buffer, void *options)
     if (input_len == 0) {
         return;
     }
-    uint8_t output[input_len];
+    uint8_t *output = InspectionBufferCheckAndExpand(buffer, input_len);
+    if (output == NULL) {
+        return;
+    }
 
     for (uint32_t i = 0; i < input_len; i++) {
         output[i] = input[i] ^ pxd->key[i % pxd->length];
     }
-    InspectionBufferCopy(buffer, output, input_len);
+    InspectionBufferTruncate(buffer, input_len);
 }
 
 #ifdef UNITTESTS